The general term glass is employed by chemists to denote all mineral substances which, on the application of heat, pass through a state of fusion into hard and brittle masses, and which, though not always transparent, exhibit a lustrous fracture when broken. The glass of commerce, however, to which our remarks are restricted, or the transparent and artificial substance which is usually distinguished by the generic name, is produced by the igneous fusion of siliceous earth with certain alkaline earths or salts, or with metallic oxides.
The etymology of the word has been much disputed. It is derived by some from the Latin glacies, i.e., its resemblance to which is thought to have suggested the title. Others have remarked, that the common Latin designation of this substance is vitrum; and as the Romans applied this term, in common with the word glastum, to the plant which we call wood, they have deduced it from the latter of these, either because the ashes of this plant were used in the manufacture of glass, or because it exhibited something of the bluish colour which is procured from wood. Glassum, the name given to amber by the ancient Gauls and Britons, has also been assigned as the origin of the word. But none of these etymons appears very satisfactory. The most plausible theory is that which derives the term from the Saxon verb glis-nian, or the German gleissen, splendere, which are probably contractions of the Anglo-Saxon ge-lizan, to shine, to be bright. This view is in a great degree confirmed by the sense in which the term glass and its derivatives are employed by our older writers, who frequently apply it to shining or glittering substances, without reference to colour or transparency.
In the most remote ages the art of blowing glass into bottles, making it into vases, colouring it to imitate precious stones, melting it in enormous masses to make pillars, rolling and polishing it into mirrors, and tinting it in parts, were all perfectly well known. For its origin we must look to Egypt, the parent of so many collateral arts. The story of the Israelites having set fire to a forest, and the heat becoming so intense that it made the nitre and sand melt and flow along the mountain side, and that they afterwards did artificially what had been the result of accident, may be set down as equally fabulous with the story of the pirates, who are said to have landed on the sea beach, and wishing to make their cauldron boil, piled up some vitreous stones and placed on them a quantity of sea-weed and blocks of wood, causing so strong a heat that the stones were softened and ran down on the sand, which melting and mixing with the alkali became a diaphanous and glassy mass. The fictitious character of both these stories is proved by the simple fact that it requires the most intense furnace heat to insure the combination of the sand with the nitre.
Under these circumstances we are justified in believing that glass-making had its origin at the same time with the baking of bricks and pottery. The smelting of ores, too, required a furnace sufficiently intense to fuse the silicates analogous to glass, and hence it may be safely inferred, that in the age when melting and working metal was known the art of making glass was also practised. In the book of Job the most precious things are compared to wisdom, but still more precious are gold and glass. The Hebrews must have become acquainted with glass while in Egypt, and in consequence of their proximity to the Phoenicians; and it is now generally believed that these two nations had the merit of originating and establishing its manufacture. The Athenian ambassadors, in order to give an idea of the magnificence displayed at the court of the great King of Persia, said, that they drank in cups of glass and gold. Some writers affirm that the Egyptians in some instances sealed up their dead in a coating of glass, and glass-houses are said not to have been uncommon in that wonderful country. Some authors ascribe, with very plausible reason, the discovery of glass-making to the priests of Vulcan at Thebes and Memphis, the greatest chemists in the ancient world. The Egyptians are also known to have made enamels of divers colours which they applied on pottery, magnificent specimens of which are still extant, and are called Egyptian porcelain. These are chiefly covered with beautiful blue or green, and groups of flowers or designs are traced in black. Glass beads and other ornaments made of that substance, skilfully manufactured and beautifully coloured, have been found adorning mummies, which are known to be upwards of three thousand years old. It is certain that Tyre, Sidon, and Alexandria, were long celebrated for their glass, and furnished the greater proportion of that used at Rome. Under the Roman Empire the Egyptians still preserved their superiority in the art of glass-making, and it is said that Aurelian caused them to pay their tribute in that manufacture. Adrian mentions that he had received drinking-glasses of various colours from a priest of a famous temple in Egypt, and gives instructions that they are not to be used but on the greatest occasions, and on the most solemn feast days. To these places the art was exclusively confined for some centuries, and was an article of luxury, being chiefly in the form of urns or drinking cups of the most elaborate workmanship, and exquisitely embellished with raised, chased, or ornamented figures. The Barberini or Portland vase, composed of deep blue glass, with figures of a delicate white opaque substance raised in relief, is a splendid specimen, and was found in the tomb of Alexander Severus, who died A.D. 285.
The art of glass-making seems to have been introduced into Italy by the Romans after their conquests in Asia in the time of Cicero, and the first glass works there were said to have been near the Flaminian Circus. It is highly probable that these workmen were imported from Egypt. The use of glass seems rapidly to have increased, and to have become very common, for we find an emperor in the third century of the Christian era saying, that he was disgusted with so low and vulgar an object as glass, and that he would only drink from vessels of gold. By this time the manu- facture of glass was so considerable that an impost was laid on it, and it was extensively employed in the decorations of buildings, while in glass mosaics were combined the most brilliant colours.
From the circumstance of coloured glass heads and amulets having been found among Druidical remains in this country, it has been argued by Pennant and others, that the art of making glass was known in Britain before its invasion by the Romans. It can hardly, however, be believed that a people who had made very trifling advances in civilization, and who, it is known, were entirely unacquainted with any other art, should be found not only conversant with the manufacture of glass, a complicated and highly ingenious process, but should excel in it; for the beads and amulets spoken of are of exquisite workmanship, and beautifully coloured in imitation of the rarest and most precious stones. There seems little doubt, therefore, that the ancient Britons procured these in the course of traffic with the Syrians, who visited the island, as we do those in the South Seas, to drive a trade with their savage inhabitants in toys and trinkets, giving them these in exchange for skins or other natural productions. By whatever means, however, these ornaments came into Britain, it is certain that they were in extensive use, though principally for religious purposes, long prior to the Roman invasion, as they are found in barrows or tumuli of a much older date. One at Stonehenge, in particular, on being opened, was found to be filled with them.
Glaive Neidyr, or Druidical glass rings, generally about half as wide as our finger rings, but much thicker, have frequently been found. The vulgar superstition regarding these was, that they were produced by snakes joining their heads together and hissing, when a kind of bubble like a ring was formed round the head of them, which the others, continuing to hiss, blew on till it came off at the tail, when it immediately hardened into a glass ring. Success was thought to attend any one who was fortunate enough to find one of those snake-stones. They were evidently beads of glass employed by the Druids, under the name of charms, to deceive the vulgar. They are usually of a green colour, but some of them are blue, and others variegated with wavy streaks of blue, red, and white.
Glass utensils have been found in Herculaneum, which city was destroyed by an eruption of Mount Vesuvius in the reign of Titus (A.D. 79). A plate of glass also found there has occasioned much speculation as to its uses. Similar plates, to which Pliny gives the name of vitreae camere, seem to have been employed, in a manner not very well understood by us, as panelling for their rooms. It is disputed whether or not glass was used in Herculaneum for windows.
Dion Cassius and Petronius Arbiter concur in their account of the discovery of malleable or ductile glass by a celebrated Roman architect, whose success in the restoration to its position of a portico which leaned to one side had roused the envy and jealousy of Tiberius, and occasioned his banishment from Rome. Thinking that his discovery would disarm the emperor's wrath, the artist appeared before him bearing a glass vessel, which he dashed upon the ground. Notwithstanding the violence of the blow, it was merely dimpled, as if it had been brass. Taking a hammer from his breast, he then beat it out into its original shape; but instead of giving him the reward which he had expected, the emperor ordered the unfortunate artisan to be beheaded, remarking, that if his discovery were known, gold would soon be held of as little value as common clay. This is probably another version of the story told by Pliny, of an artificer who made the same discovery, and whose workshop was demolished by those who had an interest in preventing the introduction of an article which would lower the value of gold, silver, and brass. Although it might not be justifiable to give unqualified disbelief to these stories, yet the knowledge we at present possess would restrict the possibility of such a discovery within the narrowest limits. The union of the properties of malleability and vitrification seems to be incompatible. Some metallic substances, by the application of intense heat, are reduced to the state of glass, but at the same time lose their malleability; which fact would seem to imply that it is impossible to communicate the latter property to glass. The extraordinary stories above mentioned have, however, been rationally enough explained by modern chemists. It has been observed by Kunckel, that a composition having a glossy appearance, and sufficiently pliant to be wrought by the hammer, may be formed; and by Neumann, that, in the fusion of muriate of silver, a kind of glass is formed, which may be shaped or beaten into different figures, and may be pronounced in some degree ductile. Blancourt, in his L'Art de la Verrerie, mentions an artist who presented a bust of ductile glass to the Cardinal Richelieu, minister of Louis XIII. But he does not seem to have been more fortunate than his predecessors; for he was doomed to imprisonment for life, for "the politic reasons," as Blancourt with much simplicity observes (we quote from the translation published in 1699), "which, it is believed, the cardinal entertained from the consideration of the consequences of that secret," which no doubt led him to fear lest the established interests of French glass manufacturers might be injured by the discovery. From expressions used by Blancourt in other parts of his work, we think, that by malleable glass, such as was produced by this artist, he understood some composition similar to those which Kunckel and Neumann discovered, and was not very exact in limiting the term to that vitreous substance which we now generally understand when we speak of glass.
The precise period at which the making of window-glass came into practice is not now certainly known. The Roman windows were filled with a semitransparent substance called lapis specularis, a fossil of the class of micra which readily splits into thin smooth laminae or plates. This substance is found in masses of ten or twelve inches in breadth, and three in thickness; and, when sliced, very much resembles horn, instead of which it is to this day often employed by lantern-makers. The Romans were chiefly supplied with this article from the island of Cyprus, where it abounds. So good a substitute for glass is it said to have been, that, besides being employed for the admission of light into the Roman houses, it was also used in the construction of hot-houses, for raising and protecting delicate plants; so that, by using it, the Emperor Tiberius had cucumbers at his table throughout the whole year. It is still much employed in Russia instead of glass for windows.
There is no positive mention of the use of glass for windows before the time of Lactantius, at the close of the third century. But the passage in that writer which records the fact (De Opif. Dei, cap. 8), also shows that the lapis specularis still retained its place. Glass windows are distinctly mentioned by St Jerome, as being in use in his time (A.D. 422). After this period we meet with frequent mention of them. Joannes Philippius (A.D. 630) states that glass was fastened into the windows with plaster.
The Venerable Bede asserts that glass windows were first introduced into England in the year 674, by the Abbot Benedict, who brought over artificers skilled in the art of making window-glass, to glaze the church and monastery of Wearmouth. The use of window-glass, however, was then, and for many centuries afterwards, confined entirely to buildings appropriated to religious purposes; but in the fourteenth century it was so much in demand, though still confined to sacred edifices and ornamental purposes, that glazing had become a regular trade. This appears from a contract entered into by the church authorities of York Cathedral in 1338 with a glazier, to glaze the west win- Glass.
dows of that structure; a piece of work which he undertook to perform at the rate of sixpence per foot for white glass, and one shilling per foot for coloured. Glass windows, however, did not become common in England till the close of the twelfth century. Until this period they were rarely to be found in private houses, and were deemed a great luxury, and a token of great magnificence. The windows of the houses were till then filled with oiled paper, or wooden lattices. In cathedrals, these and sheets of linen supplied the place of glass till the eighth century; in meaner edifices lattices continued in use till the eighteenth.
The glass of the Venetians was superior to any made elsewhere, and for many years commanded the market of nearly all Europe. Their most extensive glass-works were established at Murano, a small village in the neighbourhood of Venice; but the produce was always recognised by the name of Venetian glass. Baron von Lowhen, in his Analysis of Nobility in its Origin, states that, "so useful were the glass-makers at one period in Venice, and so great the revenue accruing to the republic from their manufacture, that, to encourage the men engaged in it to remain in Murano, the senate made them all burgesses of Venice, and allowed nobles to marry their daughters; whereas, if a nobleman marries the daughter of any other tradesman, the issue were not reputed noble."
The skill of the Venetians in glass-making was especially remarkable in the excellence of their mirrors. Beckmann, who has minutely investigated the subject, is of opinion that the manufacture of glass mirrors certainly was attempted, but not with complete success, in Sidon, at a very early period; but that they fell into disuse, and were almost forgotten until the thirteenth century. Previously to this period, plates of polished metal were used at the toilette; and in the rudeness of the first ideas which suggested the substitution of glass, the plates were made of a deep black colour to imitate them. Black foil even was laid behind them to increase their opacity. The metal mirrors, however, remained in use long after the introduction of their fragile rivals, but at length they wholly disappeared; a result effected chiefly by the skill of the Venetians, who improved their manufacture to such a degree that they speedily acquired a celebrity which secured an immense sale for them throughout all Europe.
From Italy the art of glass-making found its way into France, where an attempt was made, in the year 1634, to rival the Venetians in the manufacture of mirrors. The first essay was unsuccessful; but another, made in 1665, under the patronage of the celebrated Colbert, in which French workmen who had acquired a knowledge of the art at Murano were employed, had better fortune. But a few years afterwards, this establishment, which was situated in the village of Tourlaville, near Cherbourg in Lower Normandy, was also threatened with ruin by a discovery or rather improvement in the art of glass-making, effected by one Abraham Thevart. This improvement consisted in casting plates of much larger dimensions than it had hitherto been deemed possible to do. Thevart's first plates were cast at Paris, and astonished every artist by their magnitude. They were eighty-four inches long and fifty inches wide, whereas none previously made exceeded forty-five or fifty inches in length. Thevart was bound by his patent to make all his plates at least sixty inches in length and forty in breadth. In 1695 the two companies, Thevart's and that at Tourlaville, united their interest, but were so unsuccessful, that, in 1701, they were unable to pay their debts, and were in consequence compelled to discharge most of the workmen, and abandon several of their furnaces. Next year, however, a company was formed under the management of Antoine d'Aigincourt, who re-engaged the discharged workmen; and the works realized considerable profits to the proprietors, a circumstance which is attributed wholly to the prudent management of D'Aigincourt.
Early in the fourteenth century the French government made a concession in favour of glass-making, by decreeing that not only should no derogation from nobility follow the practice of the art, but that none save gentlemen, or the sons of noblemen, should venture to engage in any of its branches, even as working artisans. This limitation was accompanied by a grant of a royal charter of incorporation, conveying important privileges, under which the occupation became eventually a source of great wealth to several families of distinction.
It has been said that the manufacturing of window-glass was first introduced into England in the year 1557. But a contract, quoted by Horace Walpole in his Anecdotes of Painting, proves that this article was made in England upwards of a century before that period. This curious document is dated in 1439, and bears to be a contract between the Countess of Warwick and John Priddle of Westminster, glazier, whom she employed, with other tradesmen, to erect and embellish a magnificent tomb for the earl, her husband. John Prudde is thereby bound to use "no glass of England, but glass from beyond seas;" a stipulation which, besides showing that the art of making window-glass was known and practised in England in the fifteenth century, seems also to indicate that it was inferior to what could be obtained from abroad. The finer sort of window-glass was made at Crutched Friars, London, in 1557. In the year 1635, Sir Robert Maxwell introduced the use of coal fuel instead of wood, and procured workmen from Venice; but many years elapsed before the English manufactories equalled the Venetian and French in the quality of these articles. The first flint-glass made in England was manufactured at the Savoy House, in the Strand; and the first plate-glass, for looking-glasses, coach windows, and similar purposes, was made at Lambeth, by Venetian workmen, brought over in 1670 by the Duke of Buckingham. From that period the English glass manufactories, aided by the liberal bounties granted them in cash upon glass sold for export, became powerful and successful rivals of the Venetian and French manufactories. The bounty on glass exported, which the government paid to the manufacturer, was not derived from any tax by impost, or excise, previously laid; for all such were returned to the manufacturer together with the bounty, thereby lessening the actual cost of the article from 25 to 50 per cent., and enabling the English exporter to compete successfully in foreign markets. This bounty provision was annulled during the premiership of Sir Robert Peel, together with all the excise duty on home consumption.
The art of glass-making was introduced into Scotland in the reign of James VI. An exclusive right to manufacture it within the kingdom, for the space of thirty-one years, was granted by that monarch to Lord George Hay, in the year 1610. This right his lordship transferred in 1627, for a considerable sum, to Thomas Robinson, merchant-tailor in London, who again disposed of it for £250, to Sir Robert Mansell, vice-admiral of England. The first manufactory of glass in Scotland, an extremely rude one, was established at Wemyss in Fife. Regular works were afterwards commenced at Prestonpans, Leith, and Dumbarton. Crown-glass is now manufactured at Warrington, St Helens, Eccleston, Old Swan, and Newton, Lancashire; at Birmingham, Hunslet near Leeds, and Bristol. It is also manufactured of excellent quality on the Tyne and Wear. Great improvements have recently been made in the manufacture of crown-glass; and we believe this article, as made in England, is superior in quality to that of any other nation.
The manufacture of glass was introduced into the American States in 1790 by Robert Hewes, a citizen of Boston, who erected a factory in the then forest of New Hampshire. The chief aim of Mr Hewes was to supply window glass, but he did not succeed. Another attempt was made in 1800, when a factory was built in Boston for making crown window glass; but this was also unsuccessful, till a German named Lint, in 1803, took charge of the works, and the State of Massachusetts agreed to pay the proprietors a bounty on every table of window glass they made; after which the manufacture was carried on successfully, the glass steadily improving in quality, and becoming famed through all the states as Boston window glass. The same company, in the year 1822, erected new and more extensive works at Boston. The mystery attached to the art of glass-making followed it into America. The glass-blower was considered a magician, and myriads visited the newly-erected works, looking on the man who could transmute earthly and opaque matter into a transparent and brilliant substance, as an alchemist who could transmute base metal into gold.
Since the manufacture of flint glass was introduced into the eastern states there have been above forty companies formed from time to time, nearly thirty of which have proved failures. There are now ten in operation, two of which are at East Cambridge, three at South Boston, one at Sandwich, three near New York City, and one at Philadelphia. 48,000 tons of coal, 6500 tons of silex, 2500 tons ash, nitre, &c., and 3800 tons of lead are annually consumed in the manufacture of flint glass.
In the vicinity of Pittsburg, in the western states, are nine manufactories of flint glass and ten of window glass, and in the river towns are fifteen window-glass factories.
There is good reason for supposing that the art of colouring glass is coeval with the art of glass-making itself. It is certain that the art was known in Egypt at least 3000 years ago. We have already mentioned the beautiful imitations of precious stones, found adorning mummies which are known to have existed for that time. We meet with frequent mention of specimens of Eastern workmanship of consummate beauty, upon which great value was placed. The works of Caylus and Winkelmann furnish some striking instances of ancient skill in the formation of pictures by means of delicate glass fibres of various hues, which, after being fitted together with the utmost nicety, were conglutinated by fusion into a solid mass. The art of combining the various colours so as to produce pictures, such as is now practised, is comparatively of recent date. The earliest specimens of this kind of work discover a fictitious joining of different pieces of glass, differently tinged, and so arranged as, by a species of mosaic work, to produce the figure or figures wanted. The various pieces are held together generally by a vein of lead, run upon the back of the picture, precisely at their junction.
It has already been stated that the Romans combined the most brilliant colours in their mosaics; and there can be little doubt that these mosaics gave the first idea of painted or stained glass for windows in the early Christian churches. In all the early specimens of Norman glass, similar colouring and design are to be traced. Starting from the fourth century, there is frequent mention of coloured glass windows by Greek and Latin authors. St John Chrysostom and St Jerome talk of "windows of divers colours;" and Lactantius says, "that the soul perceives objects through our bodily eyes as through windows garnished with transparent glass." The early basilicas were all adorned with coloured glass, and the early Christian poets sung in ecstasies of the effect produced by the windows at sunrise. In the sixth century, Prudentia, speaking of one of these structures, says:—"The magnificence of this temple is truly regal. The pious prince who consecrated it has caused the vaults to be painted at great expense, and has clothed it with golden walls, so that the light of day may repeat the fire of the morning. In the windows is placed glass of various colours, which shine like meadows decked in the flowers of spring." An inscription on St Agnes states, that that basilica, rebuilt by the Emperor Honorius, was decorated with glass, which produced the most magnificent effect. In the sixth century, Sancta Sophia, at Constantinople, also received painted windows, which Paul the Silent praises highly. Procopius says, that day seemed to be born under the vaults of the temple; and after such glowing description it cannot be doubted that the glass was stained, not colourless.
The use of coloured glass, however, was not confined to Greece and Italy. It rapidly appeared in Gaul. Gregory of Tours, in the sixth century, also tells us that the church of St Julien de Brionde, in that town, had coloured glass windows; and the Bishop of Poictiers, describing Notre-Dame of Paris, admired the effect produced by the light falling upon the vaults and walls after passing through the painted glass, and compares it to the first tints of the morning sun.
In England, St Wilfred, who lived early in the eighth century, is said to have been the first to introduce painted glass windows, and for that purpose had workmen brought from France or Italy.
The first painted glass executed in England was in the time of King John; previously to this, all stained or painted glass was imported from Italy. The next notice of it occurs in the reign of Henry III. The treasurer of that monarch orders that there be painted, on three glass windows in the chapel of St John, a little Virgin Mary holding the child, and the Trinity, and Saint John the Apostle. Some time after, he issues another mandate for two painted windows in the hall.
Even at this early period, however, England boasted of eminent native artists in glass painting, amongst the first of whom was John Thornton, glazier of Coventry. This person was employed, in the time of Henry IV., by the dean and chapter of York cathedral, to paint the eastern window of that splendid edifice; and for the beautiful and masterly workmanship which he exhibited in this specimen of his skill, he received four shillings per week of regular wages. He was bound to finish the work in less than three years, and to receive, over and above the weekly allowance, one hundred shillings for each year; and if the work was done to the satisfaction of his employers, he was to receive, on its completion, a further sum of £10.
From this period downwards there have been many skilful native artists, although the Reformation greatly impeded the progress of the art, by banishing the ungodly ostentation of ornamented windows from churches; indeed, so serious was this interruption, that the art had nearly altogether disappeared in the time of Elizabeth. Amongst the most eminent glass painters who first appeared upon the revival of the art, were Isaac Oliver, born in 1616, and William Price, who lived about the close of the seventeenth century. This artist was succeeded by a person at Birmingham, who, in 1757, fitted up a window for Lord Lyttelton, in the church of Hagley. To him succeeded one Peckett of York, who attained considerable notoriety, but who was entirely ignorant of the true principles of the art.
During all this time, however, and indeed until a comparatively recent date, painted glass was regarded as too costly and too magnificent an article to be otherwise employed than in decorating religious edifices or the palaces of nobles; and even in the latter case it was but sparingly used. Modern improvement has placed this beautiful ornament within the reach of very ordinary circumstances; and the art of staining glass is now practised with great success, and is extensively used in decorating our domestic as well as our palatial and ecclesiastical architecture.
The colours of modern artists, we venture to allege, notwithstanding what is often urged to the contrary, equal in variety and richness those of the ancients, and, with the superior knowledge which we now possess of the principles of drawing, and of bringing several colours together on a single sheet, encouragement alone is wanting to attract artists of talent and inventive genius to the pursuit of the art, and to carry it to a greater height of excellence than it has ever reached in the hands of their predecessors.
**MANUFACTURE OF CROWN-GLASS.**
In order to secure success to his operations, the glass manufacturer must bestow the utmost care upon the erection of his furnaces. They must be well and substantially built, of the best materials, of the most approved construction, and under the direction of a builder of tried skill and extensive experience. A false economy in these respects cannot fail of leading to the most ruinous results.
Crown-glass is the best kind of glass now employed in the glazing of windows, and is so called to distinguish it from the common, broad, or spread glass, which was in use before the introduction of crown-glass, but which, on account of its inferior quality, is now rarely used. In the manufacture of crown-glass the following furnaces and arches are required, viz. calcareous arch, main furnace, bottoming hole, flashing furnace, nose hole, and annealing kiln.
A Calcareous Arch for burning frit is a common reverberatory furnace, and is about ten feet long, seven feet wide, and two feet high. A building ground plan and elevation of one is shown in Pl. CCLXXII., figs. 4 and 5. The crown and sides are built of fire-brick, and the other parts of common brick. The bottom should be carefully joined and cemented, as the salt is apt to ooze through it.
The Main or Glass-making Furnace is an oblong, built in the centre of a brick cone, large enough to contain within it two or three pots at each side of the grate-room, which is either divided, as shown in the plan, or runs the whole length of the furnace, as the manufacturer likes. Pl. CCLXXII., fig. 3 is a ground plan, fig. 2 is an end elevation, and fig. 1 a front elevation, of a six-pot furnace. 1, 2, 3, fig. 1, are the working holes for the purpose of ventilation, for putting in the materials, and for taking out the metal to be wrought. 4, 5, 6, 7 are pipe holes for warming the pipes before beginning to work with them. 8, 9, 10 are foot-holes for mending the pots and sieves. 11 is a bar of iron for binding the furnace, and keeping it from swelling.
The arch, as shown in fig. 2, is of an elliptic form. A barrel arch, that is, an arch shaped like the half of a barrel cut longwise through the centre, is sometimes used. But this soon gives way when used in the manufacture of crown-glass, although it does very well in the clay-furnace for bottle-houses.
The best stone for building furnaces is fire stone from Coxgreen, in the neighbourhood of Newcastle. Its quality is a close grain, and it contains a greater quantity of talc than the common fire stone, which seems to be the chief reason of its resisting the fire better. The great danger in building furnaces is, lest the cement at the top should give way with the excessive heat, and, by dropping into the pots, spoil the metal. The top should therefore be built with stones only, as loose as they can hold together after the centres are removed, and without any cement whatever. The stones expand and come quite close together when annealing; an operation which takes from eight to fourteen days at most. There is thus less risk of anything dropping from the roof of the furnace.
The inside of the furnace is built either of Stourbridge fire-clay annealed, or the Newcastle fire-stone, to the thickness of sixteen inches. The outside is built of common brick about nine inches in thickness.
The furnace is thrown over an ash-pit, or cave as it is called, which admits the atmospheric air, and promotes the combustion of the furnace. This cave is built of stone until it comes beneath the grate-room, when it is formed of fire brick. The abutments are useful for binding and keeping the furnace together, and are built of masonry. The furnaces are stoutly clasped with iron all round, to keep them tight. In four-pot furnaces this is unnecessary, provided there be four good abutments.
**Bottoming Hole.** Pl. CCLXXIII., figs. 3 and 4. Elevation and ground plan. The interior is of common fire-brick, the mouth either of common fire-brick or Stourbridge clay, and the outside entirely of common brick.
**Flashing Furnace.** Figs. 5 and 7. Elevation and ground plan. The outside is built of common brick, the inside of fire-brick, and the mouth or nose of Stourbridge fire-clay.
**Nose Hole.** Fig. 6. Elevation. This is a small aperture off the flashing furnace, and of the same materials. Fig. 7, ground plan.
**Annealing Kiln.** Figs. 8 and 9. It is built of common brick, except around the grate-room, where fire-brick is used.
The materials of which crown-glass is usually composed are kelp and fine white sand. Pearl ashes, or certain other alkalis, sometimes supply the place of the former of these substances. The quality of kelp is extremely various. That from Orkney is superior to what is made in Ireland, the Hebrides, or the lower parts of Scotland. It is found to contain less alkali, and to produce glass of a better colour. For the glass-maker's purposes the kelp of the Orkneys is decidedly the best. It is freer from sulphur than the others, the presence of which makes the glass green, crude, and fretful. The following is the course pursued in the preparation of kelp. The fuci are cut from the rocks in the months of May, June, and July. They are then brought to the shore, and, after being spread out and dried, are thrown into a pit lined with stones, in which a large fire of peat has been previously kindled. On this fire the weed is heaped from time to time, until a large mass is accumulated, and the whole is reduced to a state of fusion. It is then well mixed and leveled, and allowed to cool. When sufficiently cold, it is taken from the pit, and broken into portable masses, for the convenience of transportation. To prevent the dissipation of the alkali, a thing very apt to occur, the greatest care is necessary in every part of this process; in the gathering and drying, as well as in the burning of the fuci; in the treatment of the mass whilst in a state of fusion; and in its exposure to the atmosphere during these operations. Kelp burners are but too frequently guilty of carelessness in this respect. In some places they burn the fuci in pits which are not lined with stones, and, of consequence, sand and earthy substances mingle with the fused mass. It is no uncommon thing for the makers to increase the weight of kelp intentionally, foolishly thinking to procure a high-
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1 Some eminent chemists assert that, although the usual quantity of kelp be added in the manufacture of glass, the weight of the glass produced is nothing more than the original weight of the sand. But this is not the case with the Orkney kelp, for though it has less alkali, it contains more insoluble matter than the West Highland kelp, and of course produces a larger quantity of glass. The West Highland yields glass of very inferior colour to that procured by the use of Orkney kelp.
2 The best mode of preparing kelp, as invented by Colonel Fullarton, is by burning it in a reverberatory furnace, and throwing it down in the form of cakes, in the same manner as frit, which we shall afterwards have occasion to describe. When so prepared, it is more fit for the glass manufacturer, being free of extraneous matter. This method is now employed by extensive makers of kelp in Ireland. er price for it by so doing. Such adulteration is, however, at once detected by the kelp merchant, and the article, which might otherwise have brought a good price, is reduced to less than a third of its value. The inferiority of the Lowland kelp to that of Orkney and the Hebrides, may with safety be attributed as much to this practice as to the inferiority of the fuci. Some idea, but at best a very uncertain one, of the quality of kelp may be formed by the examination of its external appearance. A chemical analysis of its properties can alone give security to the manufacturer. In preparing it for the manufacture of glass, it is first broken into small pieces, either by the hand or by a machine called a stamper. It is then put into a mill and ground into a fine powder, stones and all other extraneous matter being picked out. The powder is afterwards passed through brass wire sieves.
With regard to the other component part of window-glass, namely, sand, that of the best description is procured from Lynn Regis, in Norfolk. That procured from Alum Bay, on the western coast of the Isle of Wight, is also of excellent quality. The superiority of this sand arises from the circumstance of its containing a greater quantity of minute transparent crystals than is found in the sand of any other place in the country. In preparing the sand, it is usually washed in a large vat with boiling or cold water, until the water runs off quite clear. The sand is then put into a calcining arch, where it is subjected to a strong heat for twenty-four hours. During this time it is kept red hot, and immediately on being taken out is plunged into pure cold water. This has the effect of dividing the particles of sand, and making it unite more readily with the alkali during the process of calcining. Some use nitre during this process, which consumes any sulphurous matter that may be present, or extraneous substances of an animal or vegetable nature, and reduces them to an earth not injurious to glass. When this operation is completed, it is removed into the mixing room, where the proportions of material are adjusted and mingled together, previously to their being fritted or calcined. Here the materials, the sand and the kelp powder, are carefully proportioned, generally in the degree of eleven of kelp to seven of sand, some manufacturers using eleven to eight, which are mixed up according to the judgment of the mixer. The majority of glass manufacturers are now giving up the use of kelp. Within the last few years the improvements in the manufacture of carbonate of soda have been very great, while it has also fallen considerably in price. Instead, therefore, of using such an impure alkali as kelp with sand, carbonate of soda with sand and lime is employed, which gives glass of as good a colour as plate, and is attended with many other advantages which the old materials do not possess. Manufacturers, instead of kelp, purchase sulphur, and with it make sulphuric acid. With sulphuric acid and muriate of soda they make sulphate of soda, to which lime, coal, &c., are added, and thus produce carbonate of soda, which, with sand and lime, is made into glass. The operations for preparing these materials are carried on within their own premises by several extensive glass manufacturers. The following mixture has been found to produce an excellent quality of glass:—3 cwt. Lynn sand; 2½ ditto carbonate of soda; 14 lbs. nitre; 14 ditto lime; 7 ditto charcoal; one fourth of the above weight of cullet.
This mixture will make a very excellent glass when the furnace is kept at a proper heat. The proportions must, of course, be regulated in some degree by the heat which the furnace attains. The addition of any other ingredient will injure the quality and colour of the glass. It may be either fritted or not before being put into the pots. The use of this mixture saves coals, time, and wages, as the founding occupies from sixteen to twenty hours only, whilst in other cases the time occupied by this process is from twenty to twenty-four hours. It can also be blown to a thinner and finer substance, and is thus liable to a less duty. When the sand and kelp are thoroughly mixed, the compost is put into a calcining arch or reverberatory furnace, where it is subjected to a heat so strong as to reduce it to a semifluid state. Whilst in this state, it is stirred without intermission, to prevent the formation of knots containing more sand than the rest of the batch, an effect resulting from the dissipation of the alkali by excess of heat. The process of calcining requires more or less time according to the varying properties of the ingredients composing the batch. From three to four hours is the time usually occupied by each batch. The frit, as the substance is now called, is taken from the furnace, spread upon a plate of iron whilst yet hot, and, before it becomes quite cold, divided into large cakes. In the opinion of many, it cannot be too old for use; as when new the glass made from it is full of what are called seeds. It is commonly kept about six months by opulent manufacturers. The last operation consists in throwing the frit into the melting pots, which are of the form represented in Plate CCLXXIV, fig. 2.
To prevent stones or clay from the furnace falling into the pot, those used in making flint-glass are always covered in on the top; and the same thing has been tried in crown pots, made with two openings, one in the front and one in the back, the back one to be plugged up when beginning to work from the front of the pot. This method succeeded very well, but was abandoned from the length of time it required; a circumstance which more than counterbalanced its advantages.
These pots or crucibles are made of the finest clay. That from Stourbridge in Worcestershire is considered the best. Great care is requisite in the selection, and in cleansing it from extraneous particles, the presence of which, even in the smallest degree, will injure the pot. A fine powder procured by grinding old crucibles is generally mixed, in a proportion seldom larger than a fourth, with what is termed the virgin clay. This mixture dries more rapidly, contracts less while drying, and presents a firmer resistance to the action of the fire and alkali used in the composition of glass than the mere unmixed clay. These ingredients having been mixed, they are wrought into a paste in a large trough, and carried to the pot loft, covered in such a way as to exclude dust and other minute particles. Here a workman kneads this paste by tramping it with his naked feet, turning it from time to time until it becomes as tough as putty. It is then made into rolls, and wrought, layer upon layer, into a solid and compact body, every care being taken to keep it free of vacuities, as latent air would, by its expansion in the furnace, cause an immediate rupture of the pots.
After pots are made, very great care is necessary to bring them to the proper state of dryness before taking them to the annealing or pot arch. In drying they commonly shrink about two inches in the circumference. When pots are made during summer, the natural temperature is sufficient. In winter they are kept in a temperature of from fifty to fifty-five degrees Fahrenheit. They remain in the room where they are made for a period varying from nine to twelve months. Being afterwards removed to another apartment, where the heat is from eighty to ninety degrees Fahrenheit, they are kept there for about four weeks. They are then removed for four or five days, more or less, according to their previous state of dryness, to the annealing arch (of which figs. 1 and 2, Plate CCLXXXIII. is an elevation and ground plan), which is gradually and cautiously heated up till it reaches the temperature of the working furnace, whither, after being sufficiently annealed, they are carried as quickly as possible. Pots last upon an average from eight to ten weeks. Their value is usually estimated To the frit thrown into these pots there is added a proportion, about an eighth, of cullet or broken crown-glass. After this has been done, the furnace is raised to the highest possible degree of heat. The pots are filled every third hour or so, according as the frit melts, till they are completely full. The intensity of the heat is then increased, if possible, till the metal, as it is now called, is reduced to fine liquid glass, which is then ready for the operations of the workman. From twenty-four to thirty hours in all are required for this process, which is called founding.
The furnace is slackened for about two hours, and the metal being now in a workable state, the first operator who approaches the furnace in which the pot of liquid glass is placed is the skinner, who skims off all crude or extraneous substances from the surface of the metal. Next follows the gatherer, who is provided with an iron pipe or tube, six or seven feet in length, and of this shape:
Having previously heated that end of the tube which takes up the glass, he dips it into the pot of metal; and by turning it gently round, gathers about one and a half pound of liquid glass on the end of it. Having allowed this to cool for a little, he again dips it into the pot, and gathers an additional quantity, of from two and a half to three pounds. This is also permitted to cool as before, when the operation of dipping is again repeated, and a sufficient quantity of metal, from nine to ten pounds weight, is gathered, to form what is technically called a table or sheet of glass. The rod, thus loaded, is held for a few seconds in a perpendicular position, that the metal may distribute itself equally on all sides, and that it may, by its own weight, be lengthened out beyond the rod. The operator then moulds the metal into a regular form, by rolling it on a smooth iron plate, called the "marver," a term corrupted from the French word marbre.
He then blows strongly through the tube, when his breath penetrating the red-hot mass of glass, causes it to swell out into a hollow pear-shaped vessel, thus:
The tube with the elongated sphere of glass at the end of it is then handed to the blower, who heats it a second and third time at the furnace, pressing the end, between each blowing, against the bullion bar, so called from the part thus pressed forming the centre of the sheet or bull's eye, thus:
By the dexterous management of this operation, the glass is brought into a somewhat spherical form.
The blower heats a third time at the bottoming hole, and blows the metal into a full-sized globe thus:
When this part of the process has been completed, and the glass has been allowed to cool a little, it is rested on the casher box, and an iron rod, called a "pontil" or punty rod, on which a little hot metal has been previously gathered, is applied to the flattened side, exactly opposite the tube, which is detached by touching it with a piece of iron, dipped beforehand in cold water, leaving a circular hole in the glass of about two inches diameter. The operation of attaching the punty is shown by the following plate.
Taking hold of the punty rod, the workman presents the glass to another part of the furnace called the "nose hole,"
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1 The smudger or glass gall is removed while the furnace is at its extreme degree of heat. 2 A piece of wood about eleven inches long by seven broad, with a hole three inches by one inch, forms an excellent protection to the eyes from the heat to which they are exposed when examining the metal in the pots. where the aperture made by its separation from the tube is now presented and kept until it has become sufficiently ductile to fit it for the operation of the flashing furnace. Whilst here, it is turned dexterously round, slowly at first, and afterwards with increasing rapidity; and the glass yielding to the centrifugal force, the aperture just mentioned becomes enlarged.
The workman, taking great care to preserve, by a regular motion, the circular figure of the glass, proceeds to whirl it round with increasing velocity, until the aperture suddenly flies open with a loud ruffling noise, which has been aptly compared to the unfurling of a flag in a strong breeze; and the glass becomes a circular plane or sheet, of from four to four and a half feet diameter, of equal thickness throughout, except at the point called the bullion or ball's eye, where it is attached to the iron rod. The following figure will give some idea of this very beautiful part of the process.
The sheet of glass, now fully expanded, is moved round with a moderate velocity until it is sufficiently cool to retain its form. It is carried to the mouth of the kiln or annealing arch, where it is rested on a bed of sand, and detached from the punty rod by a shears. The sheet or table is then lifted on a wide pronged fork, called a faucet, and put into the arch to be tempered, where it is ranged with many others set up edgewise, and supported by iron frames to prevent their bending. From four to six hundred tables are placed in one kiln.
A sketch of the interior of a crown-glass house, during the progress of these operations, has been given in Plate CCLXXIV., fig. 1.
The kiln having been clayed up, the fire is permitted to die out, and the heat diminished as gradually as possible. When the glass is properly annealed, and sufficiently cold to admit of its being handled, it is withdrawn from the oven, after the removal of the wall built into the front of the arch, and is then quite ready for the glazier's use. It is first, however, removed to the manufacturer's warehouse, where the circular sheets are cut into halves, and assorted into the different qualities, known to the tradesmen by the names of seconds, thirds, and fourths.
We conclude our remarks on the manufacture by observing, that the quality of glass does not depend upon the mixtures alone, but also upon the treatment it receives after it has been made, the quality of the coals, and management of the furnaces. Cleanliness in every department of the manufacture, a general knowledge of chemistry, and of the art in all its details, with the most unremitting industry, and skill in the direction and government of the operatives, are all essentially necessary for the production of good glass.
MANUFACTURE OF BRITISH SHEET-GLASS.
This article is manufactured by Messrs Chances of West Bromwich, near Birmingham, and Messrs Hartley and Company, Sunderland, who, after having visited the glass manufactories of France, Belgium, and Germany, commenced, in 1832, the making of British sheet. The principle upon which it is manufactured is the same as that acted upon in the making of common or green glass. The metal is formed into cylinders, and then flattened into sheets. The French, Belgians, and Germans, having pursued this system for the last fifty years in making their window-glass, have much improved the old mode of making it; and as the parties who are now manufacturing this article in England are crown-glass makers, and have imported all the improvements adopted in the making of sheet-glass in France, Belgium, and Germany, and combined with these the improvements which their experience as crown-glass makers had taught them during the same period, they have surpassed the French, Belgians, and Germans in sheet-glass, and can now compete with them in all parts of the world.
There is no crown-glass made in France; and their window-glass, though superior to our broad or common glass, is not equal to the British sheet. In Germany there is little crown-glass made, and that of a very inferior quality. The greater part of the glass made in that country is sheet, and it is of much better quality than the French or Belgian. In Germany a common sort of glass is made, in the following manner: Three or four workmen form a partnership, and, having fixed upon a place in the woods where clay and sand are easily met with, they proceed to build a glass-house with wood and clay. They then make the pots, and, from the ashes of the wood which they burn, obtain potash, which, after it has been mixed with sand, they melt into glass. They blow the metal into cylinders, flatten it into sheets, cut, pack, in short, perform the whole operations from first to last, themselves. A good deal of the best of the glass made in this manner is sent to Nuremberg, where it is polished and sent into Holland. Some of it is sometimes smuggled into this country, and is known by the designation of Dutch glass. The expense of making British sheet is about the same as making crown-glass, excepting in the case of large squares, when it is much less; in crown-glass it is very difficult to get a square $34 \times 22$, but in sheet-glass the common size is $40 \times 30$; nay, sheets are sometimes made as large as $50 \times 36$. Its other advantage over crown is, that it has none of that wavy or curved appearance, by which the vision is so much distorted in crown-glass; but, at the same time, sheet-glass has rather an unpleasant appearance when viewed from the outside of a building, in consequence of an unevenness of surface, technically termed coekled; when viewed, however, from the inside, it is difficult to distinguish it from plate-glass.
The materials employed in the making of sheet-glass are the same as those used in the making of crown-glass. The large melting furnace is also very similar; in France and Belgium they usually contain six or eight pots, but at the British manufactories such furnaces contain ten pots, each containing seven cwt. of metal, which requires fourteen hours to melt.
In a line with each pot, and four feet from the ground, are erected ten stages, with an open space between each, of about two feet, through which the workman swings his glass when making cylinders. When the metal is ready for working, the ten workmen take their stations, each having his own pot and stage, and also an assistant, and commence making the cylinders, as follows: After gathering the quantity of metal required (which varies from three to twenty pounds), the workman places it in a horizontal position upon a wooden block, which has been hollowed, so that, when the workman turns the metal, it shall form it into a solid cylindrical mass. In the mean time, the assistant, with a sponge in his hand, and a bucket of water by his side, lets a fine stream of water run into the block, which keeps the wood from burning, and also gives a brilliancy to the surface of the glass. The water, the moment it comes in contact with the glass, is raised to the boiling point, and, in that state, does no injury to the metal; but it is only when the metal is at a high temperature that such is the case; for, whenever the glass is cooled to a certain degree, it immediately cracks upon coming in contact with water. When the workman perceives that the mass of metal is sufficiently formed and cooled, he raises the pipe to his mouth at an angle of about seventy-five degrees, and commences blowing it, at the same time continuing to turn it in the wood block, till he perceives the diameter to be of the requisite dimensions, which are usually about ten inches. He then reheats this cylindrical mass, and, when it is sufficiently softened, commences swinging it over his head, continuing to reheat and swing till he has made it the desired length, which is commonly about forty inches. It is now in a cylindrical form, forty inches long and ten inches in diameter, one end being closed, and the other having the pipe attached to it. The workman now begins to open the end which is closed, for which purpose he encloses the air in the cylinder, by stopping the aperture of the pipe with his finger; and then placing the closed end of the cylinder towards the fire, it becomes softened, while at the same time the air within is expanding, and, in about thirty seconds, the glass becomes too soft to retain it, and bursts, a small aperture being formed at the point of the cylinder. The workman then turns the cylinder round very quickly, and, by keeping it warm at the same time, flashes it out perfectly straight; the other end, which is attached to the pipe, has now to be cut off. This is done in the following manner: The workman having gathered a small quantity of metal on the pontil, draws it out into a thread of about one eighth of an inch in diameter, laps it round the pipe end of the cylinder, and, after letting it remain there for about five seconds, withdraws it suddenly, and immediately applies a cold iron to the heated part, which occasions such a sudden contraction, that it cracks off where the hot string of glass has been placed round it. The workman having now formed a perfect cylinder of forty inches in length and ten in diameter, has, before it can be flattened, to split it on one side, so that it can be opened out; but before doing this, he is obliged to let it cool, and then, laying the cylinder horizontally upon a bench, draws a red hot iron two or three times along the inner surface. The cylinder, thus heated, immediately splits along the heated part, owing to the expansion of the glass when heated, its cylindrical form preventing its breaking at the point of expansion.
The blower having now completed his cylinder, hands it over to the flatterer to make it into a flat sheet; to accomplish which, two furnaces are built together, the one for flattening the cylinders, the other for annealing the sheets, the former being kept at a much higher temperature than the latter. The cylinder, after being gradually reheated, is placed in the centre of the flattening furnace, upon a smooth stone, with the cracked side upwards. In a short time it becomes softened with the heat, and by its own weight falls out into a flat square sheet of forty inches by thirty. The flatterer, with a piece of charred wood, rubs it quite smooth, and then places it in the annealing arch, where it remains about three days to be annealed. A workman will make sixty cylinders $40 \times 50$ in one day; and a flatterer can flatten the same number in the same time. This glass can be made of any thickness from one-twentieth to half an inch.
The same enterprising companies also manufacture extensively every variety of coloured glass used by the glass-stainer, which is gathered, rolled, blown, and flattened, in a similar way with the sheet glass, the pot-metal being gathered from one pot, and the flashed glass from two, one containing colourless and the other coloured metal, which being blown and distended together are combined, while each portion retains its individual character. These oval and square glass shades used for covering French clocks and other ornaments, as well as glass dishes for dairy purposes, are also made by these parties; and since the abolition of the glass duties are much in demand.
There is another species of glass called broad or common window-glass, which is formed of the coarsest materials. The ingredients usually employed are, six measures of soap-boilers' waste, three of kelp, and three or four of sand. After these have been fritted for from twenty to thirty hours, they are removed while red hot to the pots in the working furnace, where, in the space of from twelve to fifteen hours, they are reduced to a fluid state. The metal is taken out in the manner already described, and blown into globes about a foot in diameter. A piece of iron dipped in cold water is run along them, and produces a crack nearly rectilinear; and, while yet warm and ductile, these spheres are opened out and flattened on a smooth iron plate at the mouth of the furnace.
**MANUFACTURE OF PLATE-GLASS.**
This description of glass may be manufactured in the same manner as broad window-glass, or by casting the materials in a state of fusion upon a flat surface. Little correct information has been published relative to the manufacture of plate-glass, from the reluctance of proprietors to permit their works to be examined by individuals capable of giving an intelligible account of them. If such are permitted to scan the mysteries, they are generally restricted to keep secret the information which they have acquired. The late Mr Parks the chemist, however, seems to have been exempted from this condition, and after having visited the premises of the British Plate-Glass Company, at Ravenhead, in Lancashire, he published a short account of the process as there carried on. Besides the above manu- factory in Britain, may be mentioned that of Messrs Swinburne and Company, South Shields; the Thames Plate-Glass Company, the Union Plate-Glass Company, St Helen's; and W. A. A. West's, Eccleston. Plate-glass is also made at St Gobain in France, besides other places upon the Continent.
The following is Loyset's account of the relative proportions of the materials used at St Gobain, in the manufacture of plate-glass. White sand, 100 parts; carbonate of lime, 12 ditto; soda, 45 to 48 ditto; fragments of glass of like quality, 100 ditto; oxide of manganese, ¼. The following proportions of ingredients are said to produce the best description of this article. Lynn sand which has been well washed and dried, 720 parts; alkaline salt containing 40 per cent. of soda, 450 ditto; lime slaked and sifted, 80 ditto; nitre, 25 ditto; broken plate-glass, 425 ditto. These quantities produce one pot of metal which yields 1200 pounds of glass.
Great nicety must be observed in conducting the processes of this manufacture. The materials must be selected with the utmost care. The sand should be of the whitest and finest description, and well washed and passed through a sieve, previously to being mixed with the other ingredients. Soda is always preferred to potash, because it imparts a higher degree of fluidity to the glass, and also because the impurities which it contains are more easily dissipated by the heat. Lime acts as a flux, and manganese has the effect of giving a slightly reddish hue to the mixture by which the colours of the other materials are neutralized, so that scarcely any appreciable tint remains. Cobalt is likewise used in some manufactories, much for the same purpose as manganese. The broken glass, or cullet as it is technically called, is those fragmentary portions which are cut from the plates when they are squared, or that which may flow over in the process of casting. The sand, lime, soda, and manganese, being properly mingled in the proportions above given, are fitted in small furnaces, where the temperature is gradually raised to a red or white heat, and there maintained until no more vapour is evolved, nor change undergone by the mixture. This process occupies six hours, and after its completion the other ingredients are added, consisting of cullet and cobalt. At St Gobain there are two kinds of crucibles employed; the one in which the glass is melted is called a pot, and has the shape of an inverted truncated cone; the other is entitled a cuvette; it is kept empty in the furnace, and exposed to the full degree of heat. Forty hours are requisite to vitrify the materials properly, and bring the glass to a fit state for casting. The pots are skimmed in the manner already described. When the liquid mass has been properly refined, the cuvette is filled by a copper ladle, and after sufficient time is allowed for the bubbles created by this disturbance to escape, it is removed to the table where the plates are cast. Copper was the metal of which tables were formerly constructed; but cast iron has now been found to answer the purpose completely, and it is greatly superior to copper in this respect, that it remains uninjured during all the sudden transitions of temperature to which it must be subjected. The British Plate-Glass Company were the first to introduce this improvement. They procured a plate fifteen feet long, nine feet wide, and six inches thick. The sides are provided with metallic ribs, the depth being exactly the measure of thickness which it is desired the glass should be of. During the casting there is a similar rib temporarily attached to the lower end of the table. The cuvette being filled with melted glass, it is withdrawn from the furnace by means of a crane, taken to the upper end of the casting table, and after being properly scummed, and elevated to a sufficient height by means of a crane, it is emptied of its contents. The surface of the melted matter is then smoothed by means of a large hollow copper cylinder, which extends across the table, resting upon the side ribs. This is set in motion, and rolled over the glass, by which process it is spread out into a sheet of uniform breadth and thickness. When the plate has become completely hardened, it is carefully inspected, to see that no flaws or bubbles appear on the surface. Should any be found, the sheet is immediately divided by cutting through them. It is afterwards removed to the annealing oven, where it is placed in a horizontal position, and remains for about fifteen days. When glass is in a high state of fluidity it is liable to be injured even by a draught of air, so that the apartment must be kept as free as possible from disturbance. The opening or shutting of a door, by setting the air in motion, might impair the value of the plate. After having been withdrawn from the annealing oven, they have to undergo the operations of squaring, grinding, polishing, and silvering, before they are fit for the market. These processes have thus been described by a late writer upon the subject.
"The first process—that of squaring and smoothing the edges—is performed by passing a rough diamond along the surface of the glass, guided by a square rule; the diamond cuts to a certain depth into the substance, when, by gently striking the glass with a small hammer underneath the part which is cut, the piece comes away; and the roughnesses of the edge then left are removed by pincers. The plate is then taken to the grinding apartment.
"The next step is to imbed each of the plates upon a table or frame adjusted horizontally, and made of either freestone or wood, cementing the glass securely thereto by plaster of Paris. One plate being then reversed and suspended over another, the material employed in grinding their surfaces is introduced between the two, and they are made to rub steadily and evenly upon each other by means of machinery set in motion by a steam-engine." River sand and water were formerly used for the purpose of abrading the surface, but ground flint is now substituted, as answering the purpose better. When one side of each plate has been sufficiently ground, it is loosened from the frame, and turned over, so as to present the other surface to be ground in the same manner. Some degree of pressure is employed, by loading the upper plate with weights, as the grinding of each side approaches to completion. The process thus described used formerly to last during three entire days, but this time is now much abridged. The greatest attention is required in order to finish with the surfaces perfectly level and parallel, for which end a rule and plumb-line are employed.
By means of this grinding, the plates will have been made level; but they are too rough to receive a polish. To fit them for this, they must again be ground with emery powder of increasing degrees of fineness. The preparation and sorting of this powder are effected in the following simple and ingenious manner:—A considerable quantity of emery is put into a vessel containing water, and is stirred about violently until the whole is mechanically mixed with the water. Emery is absolutely insoluble by such means; and if the mixture were left at rest during a sufficient time, the whole would subside in layers; the coarsest and heaviest particles sinking first, and so on successively, until the very finest particles would range themselves as the upper stratum. Previously to this, however, and while these finest grains are still suspended in the water, it is poured off into a separate vessel, and the emery is there allowed to settle. A fresh supply of water is poured into the first vessel, the contents of which are again violently agitated, and allowed partially to subside as before. A shorter interval is allowed for this than in the first case; and then the liquor is poured off into a third vessel, by which means emery of the second degree of fineness is separated. This operation is repeated in order to obtain powders having five different degrees of fineness. The deposits are then separately dried upon a stove to a consistence proper for making them up into small balls, in which form they are delivered to the workmen.
"In this further rubbing together; or, as it is called, smoothing of the glass plates, it must be understood that the coarsest emery is first used, and so on, substituting powders having increasing degrees of fineness as the work proceeds."
These processes finished, the glass, although perfectly even, appears opaque or deadened on the surface, and requires polishing. This is effected in the following manner. A piece of wood is covered with numerous folds of woollen cloth, the layers being divided by some carded wool interposed between each, the whole forming a tolerably hard but elastic cushion, which is furnished with a handle. The plate is laid upon a bed of plaster, as already described, and the cushion being wetted, is covered with the red oxide of iron (the colcothar of commerce), and moved backwards and forwards upon the surface of the plate. Lastly, if the glass be intended for mirrors, it is silvered, that is, covered on one side with a thin coating of amalgam of tin and mercury.
The process of blowing plate-glass differs so slightly from the methods used in producing broad glass, that they need not be here repeated. Any difference that does exist, arises from the great bulk and weight of the mass of glass operated upon.
STAINED OR PAINTED GLASS.
In an age like the present, when a high state of civilization and refinement demands the most careful and diligent cultivation of those arts which minister to the gratification of refined taste, Glass Painting, as an art now acknowledged indispensable in the decoration of our churches, palaces, &c., has assumed an importance not attained at any former period; and from its progress in connection with our present advances in artistic knowledge, we may safely infer, that if the noble elements in its nature and capabilities be fairly and legitimately applied, it will become the most potent agent in advancing the standard of architectural decoration. Within these few years in our own country, its progress has been altogether wonderful. Since the abolition of the duties on glass, Britain has produced the rarest and the richest coloured glass in endless profusion and variety. Light has been admitted into gorgeous apartments through domes filled with coloured glass of colossal dimensions, the decorations of which, worked out from the designs of the architects, enhance and give power to the other ornamentation of the interiors, and produce a coup-d'oeil not previously known nor dreamed of. Stained-glass windows for churches have been, and are being executed in Britain, which, for appropriate design, brilliant colour, subdued tones, symmetrical proportion, minute manipulation, and variety of carefully considered detail, stand comparison with the best existing specimens of mediæval times. Windows for palatial and baronial structures have also been recently produced in this country, wherein are traced in imperishable lines, and blazoned in unfading colours, correct effigies of historical personages, representations of historical events, genealogical arrangements of heraldic bearings, and other legends and memorials, which will convey to distant times a favourable idea of the state of British art in the nineteenth century. The earliest record which we possess concerning the existence of this beautiful art is of the age of Pope Leo III., that is, about the year 800, a period in which many of the most magnificent ecclesiastical edifices on the Continent were erected. It is not known with certainty when stained glass was made use of for pictorial or figure subjects, but the historian of a monastery at Dijon, writing in the eleventh century, says, that there existed in his time in the church of his monastery some very ancient glass representing the mystery of the Holy Eucharist, and that this glass picture had been taken from the old church previous to its restoration. The earliest specimens of stained glass are composed of small pieces of glass, embued throughout with colour, united by grooved leaden joinings. It has been suggested, that this arose from the glass-makers of that period not being able to make it in larger pieces. If so, in so far as sparkling brilliancy in glass decorations is a desideratum, it might almost have been as well for the art that the manufacturers of the coloured metals had still been in the same position. Brilliancy is always increased in the same ratio with the number of pieces of glass in the composition.
Nothing could be more instructive or interesting than an investigation of the relative merits of the existing specimens of the art during the six centuries it was so diligently and effectively cultivated in connection with ecclesiastical architecture; but this inquiry would be too extensive to be opened up here. The following remarks, therefore, are confined to a few of the leading points in the glass of the various styles which prevailed in succession from the 11th to the 17th century, in which may be traced very clearly the progress of the architects, under whom the glass painters worked, from clumsy and servile imitators to bold and original designers.
The Norman style, in its early period, was a direct though imperfect imitation of Roman architecture; but when pointed architecture had attained its greatest perfection, its chief feature was originality. During the gradual development of this, its peculiar characteristic, the openings in the walls by degrees were enlarged, until they ultimately became the principal points, and it was requisite that they should be judiciously decorated; and in no branch of art connected with pointed architecture can its onward movement be more clearly traced than in the painted-glass windows.
The painted glass of the eleventh and twelfth centuries, like the Norman architecture of which it formed a part, was stately and of a magnificent character. The colours were of the most vivid and positive description. There was no spot left for the eye to repose on; no neutral tints nor secondary colours were introduced. The whole of the ground and foliage were filled with intense colour, ruby and blue invariably preponderating. The same love of violent and striking contrast as is peculiar to man in a state of semi-barbarism was manifested in the colouring of the windows of that period, and the general effect must have been congenial to the romantic and martial spirit of the age of chivalry. The leading forms were massive and simple, consisting chiefly of the circle and square, filled up chiefly with clumsy imitations of the foliated ornament to be found in Roman architecture. When figures were introduced, they were like those in the Bayeux tapestry, marvellously correct in costume, though disproportionate in drawing, and filled up with strong positive colours, flat, and the outline defined chiefly by the strong thick lines of the lead, resembling those highly titled personages represented on packs of cards, or those in Chinese processions, as delineated by the native artists of the Celestial empire.
In the thirteenth century, the painted glass, like the primary pointed or early English architecture of which it formed a part, was of a light and elegant character. The glass painter had then acquired a more correct idea of what constituted beauty, both in form and colour. The positive colours were now used more sparingly, and indeed were almost confined to geometric bands, central points, and borders continued round each entire light. The general grounds were of a beautiful tint of neutral gray, produced... by lines intersected at right angles, from which were relieved by bold lines scrolls of foliated ornament in clear colourless glass. The glass in the Sister windows of York Minster may be named as one of the finest existing specimens of this description. Figures and subjects also, when introduced, were better drawn than formerly. The faces were kept colourless, slightly shaded with brown of a rough gritty texture. The secondary colours were used in the draperies with a most delicious effect, softening and harmonizing the whole composition, and giving a lightness and variety previously unknown. In the leading forms of the ornamental portions also were seen repeated the geometric features of the building; and in the glass of the period we can recognise repetitions of the ground plans of the shafts, with the enrichments on the laps and on the mouldings of the windows and doorways. In the foliaged backgrounds, amid repetitions of the ancient Roman foliage, we now and then get fragments of simple foliage, such as trefoils, evidently taken from nature; and we are able to trace in progress an art which was shortly to become as original as beautiful, and dependent entirely on the artist's knowledge and appreciation of nature and geometry.
During the fourteenth and fifteenth centuries, when the secondary pointed or decorated style of architecture gradually developed its immense resources, and advanced steadily toward perfection, we find that the glass advanced in the same ratio as the art with which it was associated. In accordance with certain fixed rules of proportion, the glass artists elongated, intersected, diversified, and arranged rectangular, triangular, and curvilinear figures, and made these harmonious combinations their leading points for colour. They were thus enabled with certainty to produce a pleasing effect, and to fill up the detail according to their own fancy, with an imitation of the common weeds, flowers, and plants that they found growing around them. This principle was carried out in every portion of the detail in the remarkable structures then erected; and the exquisite imitations of vegetables and plants on the carving of the caps, friezes, and mouldings, show the extraordinary love of nature which must have animated these fraternities of artistic minds by whom these details were worked out. The monks of Melrose made "gude kail," says the old song, and from the exquisite manner in which that vegetable has been carved on some of the portions of that fine old abbey, one would conclude that the carvers must have shared largely and appreciated highly the "gude kail" of the holy brotherhood, a feeling no doubt also entertained by the glass painters of the structure whose works would doubtless exhibit similar genius with the glass of that period, which was well characterized by a rich juicy natural freshness, as well as an easy play of elegant outline and graceful proportion. In many instances also, the gray background produced by intersected lines was abandoned, and a tint of rough gray obscure substituted, which imparted to the whole a softer effect, and gave a better relief to the outlined foliage of which the diapering was composed. At this period also, glass painting had attracted artists of high genius, and the figures and subjects in the glass of the period are perfect specimens of what the art ought to be. These artists tested its capabilities, and how well and thoroughly they did so may be seen in Cologne Cathedral, where the flowing, bold, and elegant outline, the rough semi-transparent texture, the calm expressive countenances and attitudes of the figures of Durer and his contemporaries, fairly set aside and overpower the glowing, brilliant, but frowzy specimens there of modern German art, as practised in Munich, under the auspices of the Bavarian government. Perhaps, also, the ornamental glass of the period in that structure will be found equal to any in the world for geometrical symmetry and natural foliage, the latter imitated from the common weeds and plants indigenous to the locality. So fascinating and far-famed were the painted-glass windows of that period, so novel were the effects produced by the rich semi-transparent shadows and reflected lights, that Mr Eastlake conjectures that the increase of colour in shade which is so remarkable in the Venetian and early Flemish pictures may have been suggested by the rich and fascinating effects of the light modified by the slight shading on the stained glass through which it was transmitted. Over the Lady Chapel in the north aisle of York Minster are two windows of this period remarkable for the brilliancy and quiet feeling formerly alluded to as indispensable in glass painting of a high character.
After the decorated period painted glass degenerated first into the flat, tame insipidity of the perpendicular style, and then ran riot in the extravagant tortuosities and monstrosities of the capped, jewelled, and double gilt details of Elizabethan architecture, which it seems a fallacy to suppose was imported from Italy. At the time of its introduction a strong tide of feeling had set in against everything that pertained to the Roman Catholic religion, and it seems unlikely that after having diverged from the style with which that religion had so long been identified, the nation should have imported anything from Italy, its headquarters and chief stronghold. It rather seems probable that at a time when attempts were made to get quit of every existing form and style of architectural decoration, there would be awakened a strong desire for novelty; and when it is remembered that the newly discovered continent of America was visited by crowds of adventurers, it will not appear unlikely that many of these adventurers must have been delighted and dazzled with the magnificent and unique architectural structures which adorned the ancient cities of central America, and may have imported home and introduced into English architecture many of the features which we are accustomed to believe were originated in the Elizabethan era. The painted glass of that period partakes of the same character; and in Du Paix's great work on New Spain will be found something very like the origin of many of these peculiarities, eccentricities, and heterogeneous conglomerations which characterize the wood and stone carving, as well as the wall and window decorations of that extraordinary style of architecture.
From this rapid sketch of the history of the rise and decadence of painted glass, it appears that there is no limit to its capabilities; and that forming, as it does, a leading architectural decoration, it is as well adapted to one style as another. If the principles of harmonious colouring and symmetrical proportion be carefully attended to, as was the case in the best specimens of the art in the mediæval period, painted glass must ever be regarded as one of the most attractive decorations for church or mansion. It is no doubt a species of mosaic, and the artist must generally depend on harmonious combinations of colour and continuity and firmness of outline for the effect he intends to produce, as the brilliant colouring and mosaic character are lost in the same ratio as shading is introduced.
It is also true that windows are generally intended for the transmission of light, and that in some cases the sacrifice of light required for pictorial effect cannot be made. Yet who can resist the attractions of such pictorial glass as is to be found in the windows of St Gudule at Brussels, or St Jans Kirk at Gouda, where the principles of chiaroscuro and perspective are fully developed, where foreground and distance hold their proper places, and where the lights and brilliant colours are arranged in a manner to rival the best specimens of the ancient masters of painting in oil. This mode of treatment is not to be advocated for general use, but where there is light enough and to spare, and where men of high artistic powers apply themselves to glass painting, they may safely be left to their own genius, and allowed to render their conceptions as vividly and perfectly in glass as others do on canvas. The dull, heavy, uniform opacity which pervaded the glass of the last century, when it was made up in squares, the colours fused, and the whole work looked like cloth transparencies, is not to be tolerated. The brightest colours that can be produced in pot metals joined in the ancient way by leading ought always to be used; and although in general the effect of mosaics in low relief may be preferable, yet the shading and toning requisite to give full effect to a good pictorial design may be given without detracting greatly from the light.
Glass is the most enduring species of artistic medium, and it is to be hoped that this quality will yet cause eminent artists to leave the impress of their genius on painted windows. Had the art of painting on glass been known in the age of Phidias, we might have had preserved, in colours as vivid as when the works were executed, the Jupiter of Homer by Apelles, the pictorial embodiment of the Athenian character by Parrhasius. A singular fact illustrative of the durability of painted glass may here be stated in connection with York Minster. When the nave of that fine structure was destroyed by fire, the heat was so intense that many of the stones were calcined. When the leaden framing of the windows melted, the glass made of many small pieces fell down undamaged, and was afterwards carefully rebuilt in new leading and fixed in its original place, where it now remains the most fragile yet the most enduring portion of the ancient structure.
In ornamental painted glass the positive colours ought generally to be used sparingly, and confined to the chief points in the composition. When overloaded with colour, the sparkling brilliancy so desirable in painted glass is entirely lost. The general ground of the window should be of a neutral tint suitable in tone to its character and situation. In a southern aspect this tone should be of a cool gray, and the positive colours blue, green, and purple, ought to predominate over ruby, yellow, and orange. In a northern aspect the general ground should be of a warm sunny tint, and the warm ought to predominate over the cold colours. An eastern window ought to approximate in colour to a northern, a western to a south window.
It is always desirable to have a combination of straight and curved lines in the leading forms of painted glass. As in the human body, the effect of the elliptic curvature of the muscles is enhanced by the angular position of the straight lines on which they are placed, or by the sharp square indications of the bony extremities, in like manner the curvilinear lines in ornamental decorations appear to more advantage when balanced by a harmonious proportion of straight lines. A very important feature in glass is diapered work in the backgrounds, a great variety of designs for which may be obtained from plants and flowers by the wayside, in the field, or the garden; and the more homely these are, they are often the more suggestive and pleasing. Borderings are almost indispensable in all ornamental painted-glass windows. They bind together what might otherwise be disjointed and scattered, and afford scope for endless variety of design, both in form and colour. Heraldic symbols and emblazonments have always been amongst the most attractive features in stained-glass windows. The points which most shields form for a balance of positive colour; the crests, mantling, supporters, and mottoes, twisting or twining either quaintly or gracefully through the composition, not to speak of the interesting nature of heraldry as a guide through the intricate mazes of family connection, wending through the depths of ages—all tend to render it the most admirable field on which the glass painter can be engaged. For hall or library windows such devices are very appropriate, and indeed so highly are they appreciated, and so much is painted glass now coming into repute, that there is scarcely a new house of any pretensions without its library or staircase stained-glass window. In towns where back drawing-room windows look into mean or filthy lanes, what a delightful remedy is found in light sparkling stained glass. Either heraldic blazon, family monograms, or ornamental devices, may be used; and if the inner window be fitted up flush with the inner wall, and the room lighted at night mainly from lights placed between the outer and inner windows, the effect is chaste and beautiful.
Restorations of windows connected with ancient edifices afford fine media for embodying local legends or historical local incidents. In new structures for public purposes what place so fitting or so striking as the windows for representations of men eminent in connection with such institutions. Monumental windows have recently been introduced into churches with excellent effect, and they afford scope for invention as various as the characters of those whose virtues they are designed to commemorate. In churches even in Scotland stained glass is rapidly assuming its ancient importance, and there can be little doubt that it will ultimately be so much encouraged and cultivated that the windows of our public edifices will be the honoured medium of transmitting to remote posterity the works of the master-minds of British art.
Except in the name, painting on glass has no resemblance to any other department of the pictorial art but that of porcelain. Both the colours, and the process of their application throughout, are entirely different. While animal and vegetable substances are freely used as colouring matter in every other department of the pictorial art, they are wholly excluded in that of glass painting, where all the pigments used are subjected, after being laid on, to the operation of fire, to make them penetrate the body of the glass, or become fused on its surface—a process which would wholly destroy the colouring properties of such substances. All the colours employed in glass painting and staining are oxides of metals or minerals, as gold, silver, cobalt, which not only stand the fire, but require the powerful interference of that agent to bring out their brilliancy and transparency. Some colours, on the application of heat, penetrate the body of the glass, and, from this circumstance, are called stains; while others, being mixed with a vitreous substance called flux, become fused or vitrified on the surface. The former produces a variety of colours, and all of them are perfectly transparent. The produce of the latter are only semitransparent, but they may be made to yield any colour or tint required.
In preparing these colours, the most important point to be attended to is, to have all those that are to be used at the same time of an equal degree of softness. To attain this, those that are hard, and require a great degree of heat to make them effective, must be fixed first; leaving the soft colours, for which a slight heat only is necessary, to the last. If used promiscuously, and without regard to this precaution, some of the colours would be rendered too fluid, while others would be insufficiently fused, and the work in consequence spoiled.
GLAZING OF WINDOWS.
Putty, an important and indispensable article in the glazier's trade, is composed of whiting and linseed oil. Chalk is sometimes used instead of the former, but the expense and labour incurred in preparing it is much greater, and besides it generally contains sand, so that it is no object to the glazier to employ it. Whiting is in every way to be preferred; it must be thoroughly dried before the oil is added to it, otherwise the union will not be effected, or at least it will be very imperfect.
After the whiting has been thoroughly dried and prepared, it ought to be passed through a very fine sieve, and all the remaining lumps and knots pulverized, and then also passed through the sieve. Great care must be taken to keep the whiting free of sand and other extraneous substances.
When putty is to be made, put the proper quantity of oil into a tub or other open vessel, and gradually add the whiting whilst yet in a hot state, at the same time keeping the whole in motion with a stick, until it becomes of a sufficient consistency to admit of being wrought by the hand on a board or table. Having been removed thither from the tub, it must be wrought up with dry whiting, until it is converted into a compact mass. When brought to this state, it ought to be put into a hollowed stone or mortar, and beat with a wooden mallet till it becomes soft and tenacious, when more whiting must be added, until it has attained a proper consistency.
When putty is required of a superior degree of fineness, and which will also dry quickly, add a little sugar of lead or litharge; and if an increase of strength be wanted, a little white lead.
When the panes have been fitted into the cheeks of the sashes, they must be removed, and the cheeks well bedded with beat putty. This done, the panes are again returned to their places, and gently pressed or lodged in the bedding, the workman, as it were, humouring the glass should it be bent or twisted, and taking care that there is no hard extraneous substance mingled with the putty, which might endanger, if not actually break, the glass. When a pane is perfectly bedded it lies quite firm, and does not spring from the putty; but when, either from a perverse bend or twist in the glass, or any other accidental cause, it happens that it cannot be made to go quite close to the cheek, the vacant space must be carefully and neatly filled upon the back puttying, otherwise the window will not be impervious to the weather, and will be very apt to fall into decay by the admission of moisture.
The convex or round side of the pane, where such a shape occurs, should be presented to the outside, and the concave or hollow to the inside. When thus placed, they resist the weather better than if the hollow sides were exposed to it.
After the pane has been bedded, the next process is the outside puttying. This putty should be kept in the fore cheek, about the thirty-second part of an inch below the level of the inside cheek, so as to allow the thin layer of paint which binds these two substances together to join the putty and glass; and that it may not offend the eye by being seen from the inside; and that, when it is painted, the brush may not encroach on any visible part of the pane, leaving those ragged lines or marks which are so often seen from the inside on ill-finished windows, and which are so displeasing to the eye. This operation, and finishing the corners, are two nice points in the art, and therefore, when properly done, discover the neat-handed and skilful workman.
All frames or sashes of windows ought, before being glazed, to receive one or two coats of white paint, to which a small portion of red lead has been added to facilitate its drying, and to give increased strength and durability to the paint.
Lattice or Lead Windows.—This antique and singularly beautiful style of glazing has unaccountably fallen much into disuse, although of late years it has certainly undergone something like a resuscitation, in consequence of a revival of the public taste for stained glass, and a growing predilection for Medieval architecture in churches, cottages, and the like. For these, and for staircase windows, and indeed all windows similarly situated, as in halls, lobbies, or the like, it is peculiarly adapted.
It may be proper to premise, that lead windows require stained or coloured glass for producing their fullest and best effects, and it was with stained glass only that they were originally constructed; but very neat and elegant windows are executed in this style with plain glass, where variety and beauty of figure are made to compensate in some measure for the absence of colour.
Lead windows may be made to any pattern, and in this there is great scope for the display of a correct taste. In the time of Elizabeth, this branch of the glazier's art was carried to great excellence, especially by one Walter Geddes, who was employed in glazing most of the royal and public buildings of that period. Geddes executed in this style some windows of transcendent beauty, displaying an endless variety of the most elegant and elaborate figures. The most useful and most common description of plain glass lead windows, however, are those of the diamond or lozenge shape; but, as already said, they may be made to any pattern desired.
The lead work can be adapted with ease to any pattern that may be chosen for the glass; and it can likewise be made to any breadth, from one-eighth to five-eighths of an inch.
The apparatus and tools necessary for producing this are, a glazier's vice, or lead mill, moulds for casting the lead into slender bars or rods of about eighteen inches in length, which is the first process; a three-fourth inch chisel; a hard-wood fillet for forcing the glass into the grooves in the lead frame-work; and an opener or wedge tool, made also of hard wood, or ebony, for laying open the grooves for the reception of the glass; two copper bolts for soldering, the end formed like an egg. A correct delineation of the vice or mill alluded to is given in Plate CCI.XXV., in describing which, in its various connected parts, the same letters of reference are adapted to the different figures, so far as necessary, which, with the isometrical views, will facilitate the comprehension of their parts and properties.
Fig. 1, an end view, partly open, of a mould for casting three varieties of patterns, which are thus prepared for being forced through the machine. By an ingenious construction of the handle, it is made to lock and unlock by inclined planes, acting on studs aa. Fig. 2, a side view, also partly open; and fig. 3, an isometrical view of the mould prepared for pouring in the metal.
The metal or cast being removed from the mould, a pair of the dies (one only of each pair is represented), according to the pattern required, figs. 4, 5, 6, 7, are placed in the machine, as seen at cc; fig. 8, isometrical view. After they are put in, a thin iron cover (b, fig. 10), with an oblong hole in the middle, is put on to guide the metal into the rollers. Figs. 9, 10, and 11, represent three views of the machine as prepared for operating. In figs. 9 and 11, the metal dd is represented passing through the machine, which is accomplished by turning the winch handle ee, acting on two equal-sized toothed wheels ff. On the axles of these are two rollers gg, slightly serrated (dotted through in figs. 8 and 10); these rollers draw the metal through, while the dies give the desired form. To allow the axles and rollers to be placed in the frame or body of the machine A, the cover h is removed by unscrewing the bolt i, figs. 8, 10, 11. The toothed wheels ff are also taken off, by unscrewing the nuts kk. The tempering screw bolt l is for adjusting the dies after they are put in their place. The screw bolts mm are for fixing the machine to a table or bench.
Fig. 12 is an isometrical view of the cover h, removed to show the ports nn, through which the axles of the rollers pass.
Fig. 13 shows the shape of the bolt used for soldering the lead windows, and fig. 14 the opener already described.
The lead intended to be employed in window-making must be soft, and of the very best quality; and great care must be taken to have the moulds properly tempered, otherwise the lead will not be equally diffused in them, and the castings consequently not perfectly solid throughout, as they ought to be. The castings are, as already noticed, usually about eighteen inches in length, and are afterwards extended by the mill represented by the figure above, to the length of five or six feet.
It may not be unnecessary to add, that the mill not only extends the lead, and reduces it at the pleasure of the operator to the dimensions required, but at the same time forms the grooves into which the edge of the glass is afterwards introduced in forming the window.
When the lead has been prepared in the manner described, the glazier ought to proceed to cut out the panes wanted. For this operation he must prepare by first outlining the full dimensions of the window, and then lining it off to the pattern required, shaping the panes accordingly. If the window is of a large size, this may be done by compartments, to be afterwards united, and thus be more conveniently wrought.
When all the glass has been cut for the window, the next thing to be done is to open the grooves in the lead with the opener or wedge tool. The panes are then, in order that they may be water-tight, fastened very firmly into the grooves with the wooden fillet already spoken of (which may be fixed on the handle of the chisel or cutting tool), the parallel lines of lead being secured in their proper places on the board, when the window is of the diamond shape, by a small nail at either end, until the course is finished, when the work is permanently fastened by running a small quantity of solder gently over the two connecting pieces of lead at each joint, or angular point. When the window has been completed, it should be removed from the working board to a flat table, and there covered with a thick layer of cement, composed of white lead, lamp black, red lead, litharge, and boiled linseed oil, with a half-worn paint-brush, and the composition carefully rubbed into every joint. This will render the window completely impervious to the weather, as the cement, if properly laid on, will fill every crevice, where it will soon become as hard and durable as any other of the materials of which the window is composed.
The window, on being fitted into the frame, that is, on being set in its place in the building for which it is intended, ought to be supported with iron rods, extending three-eighths of an inch beyond the breadth of the frame on each side, running across it at the distance of from twelve to fourteen inches from each other, and secured to the lead frame-work at intervals with copper wire.
THE CUTTING DIAMOND.
Before the introduction of the diamond as an agent in cutting glass, that operation was performed by means of emery, sharp pointed instruments of the hardest steel, and sometimes red-hot iron. These were the only contrivances known and practised by the ancient glaziers.
In considering the diamond in its relations to the purposes of the window-glass cutter, there occur some circumstances not unworthy of remark. Amongst these, it may be noticed, that the cutting point of the diamond must be a natural one; an artificial point, however perfectly formed, will only scratch the glass, not cut it. The diamond of a ring, for instance, will not cut a pane, but merely mark it with rough superficial lines, which penetrate but a very little way inwards. Artificial points, corners, or angles, therefore, produced by cutting the diamond, are adapted only for writing or for drawing figures on glass, and such were those used by Schwanhard, Rost, and the other old artists who were celebrated for ornamenting glass vessels. The cutting diamond does not write so well on glass, from the circumstance of its being apt to enter too deeply, and take too firm a hold of the surface, and thus become intractable. It may further be noticed, that an accidental point produced by fracturing the diamond, is as unfit for cutting as an artificial one. Such a point will also merely scratch the glass. No point, in short, that is not given by the natural formation of the mineral, will answer the purposes of the window-glass cutter.
The large sparks, as the diamonds used for cutting glass are called, are generally preferred to the small ones, from the circumstance of their being likely to possess (although this is by no means invariably the case) a number of cutting points; while the very small sparks are not always found to possess more than one. Thus, if the point of the latter is worn or broken off, although the spark be turned, and reset in its socket, it will still be without the power of cutting, and consequently useless; while the former, on undergoing the same operation, will present a new and effective point.
The large sparks are called mother sparks, and are sometimes cut down into as many smaller fragments, bearing the same name, as there are natural points in them. Each of these, therefore, can have only one cutting point, and are consequently only proportionately valuable to the glazier, since they cannot be restored by resetting.
The Setting of Diamonds is a process with which every glazier ought to be acquainted; nor is it an art of difficult acquirement; some practice, and a little patience, are all that is necessary.
After having selected a stone, as clear and pellucid as possible, and of an octahedral shape, or as near to that form as it can be procured, the workman proceeds to ascertain which is its cutting point, or, if it has more than one, which is the best. This will be found to be that point which has the cutting edges of the crystal placed exactly at right angles to each other, and passing precisely through a point of intersection made by the crossing of the edges.
He then provides a piece of copper or brass wire, a quarter of an inch in diameter, having a hole drilled in one of its ends large enough to contain three-fourths of the diamond to be set. Having temporarily secured the diamond in this hole, the setter ascertains the cutting point by trying it on a piece of glass; and when he has discovered it, he marks its position by making a slight notch in the wire with a file or otherwise, exactly opposite to the cutting point, as a guide to him in his operations when he comes to fix it permanently in the socket head of the handle. When doing this, care is taken to keep it exactly parallel with the inclined plane of the socket head.
The cutting point having been ascertained, and the diamond fixed into its place, the wire is then cut off about a quarter of an inch below the diamond, and filed down to fit exactly into the aperture in the socket head, into which it must be soldered. The rough or superfluous metal around the stone is removed with a file; and, lastly, the setting is polished with emery or sand paper. Such is the most approved method of setting new diamonds, and it applies equally to the resetting of old ones. But in the latter case, the first process, that of detaching the stone from its bed, is accomplished either by means of a knife, or by applying the blowpipe.
The art of managing the diamonds in glass-cutting, so as to produce effective results, can only be attained by considerable experience. The diamond must be held in a particular position, and with a particular inclination, otherwise it will not cut, and the slightest deviation from either renders an attempt to do so abortive. In the hands of an inexperienced person it merely scratches the glass, leaving a long rough furrow, but no fissure. The glazier judges by his ear of the cut made. When the cut is a clean and effective one, the diamond produces, in the act of being drawn along, a sharp, keen, and equal sound. When the cut is not a good one, this sound is harsh, grating, and irregular. On perceiving this, the operator alters the inclination and position of his diamond, until the proper sound is emitted, when he proceeds with his cut.
The diamonds employed in glass-cutting are of the description known by the technical name of bort, a classification which includes all such pieces as are too small to be cut, or are of a bad colour, and consequently unfit for ornamental purposes. These are accordingly selected from the better sort, and sold separately, at an inferior price.
Though there are many substances that will scratch glass, the diamond was thought to be the only one that would cut it; but some experiments of Dr Wollaston have shown that this is not strictly correct. That eminent philosopher gave to pieces of sapphire, ruby, spinel ruby, rock crystal, and some other substances, that peculiar curvilinear edge which forms the cutting point in the diamond, and in which, and in its hardness, its singular property of cutting entirely lies, and with these succeeded in cutting glass with a perfectly clear fissure. They lasted, however, but for a very short time, soon losing their edge, although prepared at a great expense of labour and care; while the diamond comes ready formed from the hand of nature, and will last for many years.
**MANUFACTURE OF FLINT-GLASS OR CRYSTAL.**
This branch may be defined the art of forming useful and ornamental articles of glass, and is the most ancient department of glass manufacture. The manipulatory processes have scarcely been varied and only slightly extended since the earliest times. The progress of chemistry has supplied purer materials but introduced few new ones. Thus we find that baryta has replaced the lead, and soda the potash in ancient glass, while in the production of coloured glasses purer and additional metallic oxides are used. Yet this art has shown less tractability in the hands of the improver than perhaps any other industrial art.
The best flint glass or crystal is composed of silica, potash, and lead, the average proportion being one-half sand, one-third red lead or litharge, one-sixth carbonate of potash, and a little saltpetre, manganese, and white arsenic to correct and improve the colour or accidental impurities of the other materials. For inferior glass, or "tail metal" as it is technically called, soda is substituted for potash, and baryta for lead or litharge. In still cheaper "metal" for common small phials or bottles, a mixture approximating that for window-glass is used. For optical purposes the proportion of lead is increased to improve the refractive properties, which increase in proportion to the density of the medium. The specific gravity of the metals varies from about 3·6 to 2·5.
The furnaces employed are generally circular, and contain eight or ten pots of the form represented in fig. 2, Plate CCLXXVI. The "found," as the period of melting the materials is termed, commences generally on a Friday evening. The materials or "batch," and a portion of broken glass or "cullet" being mixed together are gradually introduced into the heated pot. Fig. 1, Plate CCLXXVI. represents the interior of a glass-house; the building in the centre being a large cone or chimney built over and around the furnace which is seen through the arches α. The holes into which the men at 5 and 6 are dipping iron tools are the openings through which the batch is introduced and the metal withdrawn. The grate is in the centre of the furnace, and there are flues at the back of the piers between the arches. As the batch melts there is a considerable evolution of gases, which at length subsides, when the metal begins to "fine" and reaches the "crisis." It is then cooled until about the consistency of thick honey. The evolution of the gases disperses air bubbles through it; and the glass-maker endeavours so to regulate the heat of the furnace that the bubbles may rise to the surface, burst, and leave the metal plain and fine, but if the heat be continued beyond the crisis, the quality of the metal is deteriorated.
For some time after the greater part of the gas has escaped, little bells or beads, technically called "seeds," rise and are extricated more freely by agitation or alteration of temperature. If the metal becomes solid while these bubbles are rising, it retains them, and if the "crisis" is not quickly passed, although the seed may be overcome by long continued fusion yet bad colour and other defects arise. Strings and striæ, which upon close examination may be found in nearly all glass, are very common and troublesome. They may be caused by improper mixing of the materials, separation in the pot of metal of different densities, large grains of sand or pieces of refractory clay. But as strings and striæ in clear ice give pure water when melted, so in glass, mechanical rather than chemical means must be used for their prevention and cure. For optical glass Bontemps has carried out the recommendation of Faraday, and by systematically stirring the fluid glass has nearly reduced the manufacture of optical glass for large lenses to a certainty.
Crystal glass is popularly called colourless, but a practised eye quickly detects colour, which is more readily perceptible in the mass. It is probable that even pure silica, oxide of lead, and carbonate of potash will not produce colourless glass, but that there is a colour proper to glass as there is to air and water. But the main causes of colour in crystal are slight impurities, consisting of the oxides of iron or compounds of sulphur or carbon. A large excess of lead gives a yellow colour,—the oxides of iron, orange or olive-green tints, and compounds of sulphur or carbon, orange or blue. The peroxide of iron gives orange of a light tint, compared with the olive-green produced by the same quantity of the protoxide of iron. The addition of the black oxide of manganese or of saltpetre, produces purple, peroxidizes the oxide of iron, and, combined, forms what is called white, but practically an approach to black, and by a large dose of these materials glass of opaque blackness may be produced. Saltpetre also peroxidizes the iron, and heightens the colour due to manganese. Purity of materials is essential to success, and oxide of manganese was formerly called glass-makers' soap; but although it reduces the colour arising from iron, it does not annihilate it. Glass rendered colourless by manganese becomes pink by exposure to the direct rays of the sun, and if too much is used in the "batch" the metal is rendered pink, and is called high-coloured. Glass with too little manganese has a "low colour." The high colour may be reduced by the deoxidizing agency of a pole of wood, with which, in such case, the metal is stirred. Some of the high colour is lost in the annealing, and thick vessels remaining long in the "leir" or oven lose more than the light articles which are passed quickly through; therefore to obtain equality of colour, the metal for thick goods must be highest coloured. Arsenious acid is also employed as a corrective of colour. Sulphur is a powerful agent in colouring glass. Sometimes a pot of metal foams while melting and is of a dark amber or orange colour, which occasionally it retains when cool, or at other times changes to the light blue tint of the common soda-water bottle. Both tints are caused by the presence of sulphur, the orange by the larger quantity. One part of sulphur to two hundred of glass produces a dark colour; hence, by adding a sulphuret to the melted metal the tints can be deepened at will. Splitgerber shows that glass containing one of sulphur in three hundred of glass becomes at a moderate low red heat nearly black and opaque, but becomes more transparent at a higher temperature. Similar changes are produced by heat on sulphur in its pure state. At its melting point it is lemon-yellow; at higher temperatures it becomes orange, and gradually deepens nearly black, and at a still stronger heat is volatilized in yellow vapours. Similar results are obtained with glass coloured by gold, silver, and copper; glass co- Glass.
loured by sulphur takes a deeper stain from silver than other glass, but if overheated becomes a light greenish-yellow on the reverse, and dark chestnut on the obverse, and is rendered useless. In Bohemia, glass consisting only of potash, silica, and lime is stained of a bright scarlet colour by copper; the process is not followed in Britain probably in consequence of British glass always containing lead or soda.
The metallic colours used for flint glass are cobalt for blue; chromium or a mixture of iron and copper for green; manganese for purple; copper for deep scarlet or light blue; gold for crimson; antimony or iron for yellow; uranium for topaz. Glass coloured by the oxide of uranium exposed in a dark room to the dim light of the electric Aurora becomes translucent and illuminated throughout, and is partially so when exposed to the hydrogen flame. White enamel is obtained by the addition of oxides of arsenic, tin, fluor spar, or phosphate of lime, and coloured enamels are produced by adding the appropriate metallic oxides.
In the manipulation of the glass the men are arranged in sets of four, called chairs, and there are generally four chairs to a furnace. The principal workman of each chair is called the gaffer, the second the seretor, the third the footmaker, and a boy completes the set. The wages of these men vary from 60s. to 20s. per week. The work is heavy, and requires such skill and dexterity that few first-class workmen are found. The men work in six-hour shifts, there being a complete double set. The first operation of the glass-blower is to skim the metal, as most impurities float on its surface, and this is done with an iron rod heated at its extremity and dipped into the metal, a little of which adheres. This is flattened on an iron plate and repeatedly introduced, gradually growing larger until it gathers and removes all the floating matter from the surface of the metal. The operation of making crystal articles then goes on as follows.
An iron tube is heated at the end and dipped into the semifluid metal, see Plate CCLXXVI. figs. 5 and 6, a portion of which is collected, withdrawn from the pot, and then rolled on an iron plate called the marver, as in fig. 7, until it has acquired the circular shape seen there. The marver also equalizes the heat of the gathering, which the iron tube cools and stiffens, and which requires to be equally ductile in all its parts. The servitor now prepares a post, as a flattened round hot lump of metal on a punty or iron rod is called, and applies it to the end of the globe as shown in fig. 9. The two masses of glass are thus united together, and that attached to the hollow tube is separated by touching it, near to where the tube enters the globe, with a small piece of iron wetted with water. By this means the glass cracks, and a smart blow on the iron tube completes the disunion. The workman now takes the punty from his assistant, and laying it on his chair arm, rolls it backward and forward with his left arm, while with his right he moulds it into the various shapes required, by means of a very few simple instruments. By one of these called a procello, the blades of which are attached by an elastic bow like a pair of sugar tongs, the dimensions of the vessel can be enlarged or contracted at pleasure. Any superfluous material is cut away by a pair of scissors. For smoothing and equalizing the sides of the vessel a piece of wood is used. After the article is finished it is detached from the punty and carried on a pronged stick to the annealing oven or leir, a representation of which is given in Plate CCLXXVI. fig. 3.
For a fluted or ribbed cane, as a solid glass rod is technically called, the metal is forced into a mould of the requisite shape and then withdrawn; after which, if attached to another post and the two punties be twisted and drawn in opposite directions, the ribs become spiral lines, which become more acute as the drawing is extended. Venetian filigree work is produced in this way; and if in the hollow flutes of the mould coloured glass or enamels are inserted, and the ga-
thering introduced, the coloured glass or enamels are welded to and withdrawn with it. When again heated, and twisted or drawn, these streaks of colour or enamel become spiral, and ornament the surface. If before being drawn the mass be redipped into the pot of crystal glass and then twisted, the spiral lines of colour or enamel become internal. By the repetition of this process spirals can be formed within spirals, and by placing these filigree canes side by side and welding them together, very curious and intricate patterns are obtained. By the ordinary process of blowing, vessels are formed with smooth and concentric interior and exterior surfaces, and do not exhibit the brilliancy of the crystal so much as when it has numerous inequalities. The most brilliant effect is produced by cutting, but moulding is much cheaper, and this branch of the art has now reached a high state of excellence. The moulds are generally of iron highly polished, and are kept a little below a red heat. The surface of the metal is injured by contact with the mould, but its transparency is restored by being reheated. A very exact regulation of the temperature is necessary in reheating fine mouldings; too little heat does not give the "fire polish," too much softens the metal and obliterates the mouldings. The moulds for pressed goods are made in pieces so hinged or connected as to close and leave a vacancy, the form of the article required, the hollow in which is not however produced by blowing but by the plunger of the press under which the mould is placed. The required quantity of metal is then dropt in, when the plunger descends and forces it into all parts of the cavity, completing the formation of the article, which is then stuck to a punty, and fire-polished and annealed.
What is called cased glass is crystal covered with coats of coloured glass. It is thus obtained. The gathering of crystal is thrust into a coloured or enamelled shell, which is previously prepared. The welding is completed by reheating; and two or more coats of different colours or enamels may thus be employed. When cut through to the crystal in various figures, the edges of the different colours on enamel are seen.
The Venetian frosted glass is obtained by immersing the hot metal gathering in cold water, quickly withdrawing it, reheating and expanding it by blowing, before it becomes so hot as to weld together the numerous cracks on the surface caused by the cold water. These cracks only penetrate where the metal has been cooled by the water, and remain as depressions until the article is finished.
Venetian vitro-di-trono consists of spiral lines of enamels or colours, crossing each other diamond-wise, in the body of the glass, and inclosing an air-bubble in the centre of each diamond. It is thus formed: a gathering is blown in the mould with the necessary canes twisted and blown out as formerly described for spiral filigree, the canes being left projecting from the outside like ribs or flutes. A similar piece is made and turned inside out. The projecting canes on this piece are inside, and the spiral lines reversed. The one piece is then placed under the other, and both are welded together. The ribs or flutes projecting from the two surfaces in contact inclose air in the diamonds, which gradually assumes the bubble shape. The vessel is then formed in the ordinary manner. The most beautiful regularity of lines is thus obtained; and when the ends are closed by the procellos, the lines are drawn to a centre as regularly arranged as if they had been turned in an engine.
Incrustations are formed by placing the substance to be inclosed on the surface of the article, and dropping melted metal on it, or by preparing an open tube of glass, inserting the object, and welding the open end. By suction instead of blowing, the metal is collapsed on the object, and the air withdrawn. From the unequal contraction between the object and the crystal by which it is surrounded there is much difficulty in the annealing, and to avoid the risk of breakage the object should be made of materials expanding and contracting like the glass itself.
The round, heavy paper weights containing various ornaments apparently in the body of the metal are made as follows:—Canes are made to the required pattern—say, for example, a star within a tube. A gathering of white enamel is formed in a star-shaped mould, and coated with crystal. After this is marvered; it is dipped into a coloured enamel, and drawn out into a cane; and if this is covered with crystal, the eye cannot detect the junction of the external crystal with that of the cane, but the enamel casing will appear as a tube with the star standing in the centre. Devices of numerous kinds are thus made in canes, and then welded together. The end is then ground, and, after being heated and incased in crystal, the lens-like shape of the paper weights adds to the effect by magnifying the incrustated canes.
The light-refracting properties of crystal are best shown by cutting and polishing. Fig. 4, Pl. CCLXXVI., represents a glass-cutter's mill. A is the pulley and band communicating motion to the mill, which is made of wrought or cast iron. Stones of various textures, or wood, sand, or emery, in water, are used with the metal mills, water only with the stones, and pumice-stone and putty-powder with the wood for smoothing and polishing. The articles are held in the hand, and applied to the mill while rotating. The punty marks are ground off tumblers, wine-glasses, and such like, by boys holding them on small stone mills. Ground or frosted glass is made by rubbing the surface with sand and water. Iron tools fixed on a lathe and moistened with sand and water are used to rough out the stoppers and necks of bottles, which are completed by hand with emery and water. The neighbourhood of the coal-fields is of course the chief seat of the manufacture, and probably the best crystal is now made in Manchester.
**BOTTLE-GLASS.**
Plate CCLXXIV., fig. 4, is a ground-plan, showing all the necessary buildings for two bottle-houses, and in one of the houses the ground-plan of a four-pot furnace and ash arches. The furnace is an oblong, similar to what we have described the crown-furnace to be, but arched over in the barrel shape. It is erected in the centre of the brick cone, above a cave, which admits the atmosphere to the grating. The working holes of this furnace, opposite each pot, for putting in the materials and taking out the liquid glass, are each about one foot in diameter. At each angle of the furnace there is also a hole about the same size communicating with the calcining arch, and admitting the flame from the main furnace, which reverberates on and calcines the materials in the arch. Fig. 1 shows the main furnace; 2, 3, 4, 5, the ash arches for calcining the materials; 6, 7, 8, 9, 10, 11, annealing arches; 12, two-pot arches; 13, what is considered an improved plan; 14, clay-house, for picking, grinding, sifting, and afterwards working the clay into paste for the purpose of manufacturing pots; 15, mill house for grinding clay; 16, a building containing a calcar furnace for experiments, or for preparing the materials, when the ash arch attached to the main furnace is under repair, including, 1, a sand crib, and, 2, an ash crib for sitting and mixing the materials, sufficient for two houses.
The common green or bottle-glass is made of the coarsest materials; sand, lime, sometimes clay, any kind of alkali or alkaline ashes, whose cheapness may recommend it to the manufacturer, and sometimes the vitreous slag produced from the fusion of iron ore. The mixture most commonly used is soap-maker's waste, in the proportion of three measures to one measure of sand. The green colour of this glass is occasioned by the existence of a portion of iron in the sand, and, it may be, also in the vegetable ashes of which it is composed.
When castor-oil or champagne bottles are wanted, a portion of crown-glass cullet is added, to improve the colour. The impurity of the alkali, and the abundance of fluxing materials of an earthy nature, combined with the intense heat to which they are subjected, occasion the existence of but a very small proportion of real saline matter in the glass, and thereby render it better than flint-glass for holding fluids possessing corrosive properties.
The soap-maker's waste is generally calcined in two of the coarse arches, figs. 3 and 4, which are kept at a strong red heat from twenty-four to thirty hours, the time required to melt the materials and work them into glass, which is termed a journey. After the soap-maker's waste is taken out of the arch, it is ground and mixed with sand in the proportions already mentioned. This mixture is put into the fine arches, and again calcined during the working journey, which occupies about ten or twelve hours more. When the journey is over, the pots are again filled with the red-hot materials out of the fine calcining arch. Six hours are required to melt this additional quantity of materials. The pots are again filled up, and in about four hours this filling is also melted. The furnace is then kept at the highest possible degree of heat, and in the course of from twelve to sixteen hours, according as the experience of the founder may determine, the materials in the pots are formed into a liquid glass fit for making bottles. The furnace is now checked by closing the doors of the cave, and the metal cooling, it becomes more dense, and all the extraneous matter not formed into glass floats upon the top. Before beginning to work, this is skimmed off in the way already described in our account of crown-glass making. A sufficient quantity of coals is added at intervals, to keep the furnace at a working heat till the journey is finished.
After the pots have been skimmed, the person who begins the work is the gatherer, who, after heating the pipe, gathers on it a small quantity of metal. After allowing this to cool a little, he again gathers such a quantity as he conceives to be sufficient to make a bottle. This is then handed to the blower, who, while blowing through the tube, rolls the metal upon a stone, at the same time forming the neck of the bottle. He then puts the metal into a brass or cast-iron mould of the shape of the bottle wanted, and, continuing to blow through the tube, brings it to the desired form. The patent mould now in use is made of brass, the inside finely polished, divided into two pieces, which the workman, by pressing a spring with his foot, opens and shuts at pleasure. The blower then hands it to the finisher, who touches the neck of the bottle with a small piece of iron dipped in water, which cuts it completely off from the pipe. He next attaches the punty, which is a little metal gathered from the pot, to the bottom of the bottle, and thereby gives it the shape which it usually presents. This punty may be used for from eighteen to twenty-four dozen of bottles. It is occasionally dipped into sand to prevent its adhering to the bottle. The finisher then warms the bottle at the furnace, and taking out a small quantity of metal on what is termed a ring iron, he turns it once round the mouth, forming the ring seen at the mouth of bottles. He then employs the shears to give shape to the neck. One of the blades of the shears has a piece of brass in the centre, tapered like a common cork, which forms the inside mouth; to the other blade is attached a piece of brass, used to form the ring. The bottle is then lifted by the neck on a fork by a little fellow about ten years of age, and carried to the annealing arch, where the bottles are placed in bins above one another. This arch is kept a little below melting heat, till the whole quantity, which amounts to ten or twelve gross in each arch, is deposited, when the fire is allowed to die out. GLA
Burning Glass. See Burning Glasses.
Looking Glass. See Mirror, and Foliating of Looking-Glasses.
Musical Glasses. See Harmonica.
Weather Glass. See Barometer.
GLASSITES or Sandemanians, a religious sect that first appeared in Scotland about A.D. 1728, when Mr Glass, a minister of the Scottish Established Church, avowed opinions on church government approaching very nearly to those of the Congregationalists. About 1757 Robert Sandeman appeared as an advocate of the same opinions, and in 1762 he organized a congregation. The prominent distinguishing doctrine of the Glassites relates to the nature of justifying faith, which Sandeman maintained to be "no more than a simple assent to the divine testimony passively received by the understanding." Certain peculiar practices also are observed by this sect, which are by them supposed to have been prevalent among the primitive Christians, such as weekly communions, love-feasts, mutual exhortations, washing each other's feet, plurality of elders, the use of the lot, and several others.
In 1851 the number of Glassite congregations in Great Britain was twelve, with aggregate accommodation for about 2000 persons.