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 checks of the sashes, they must be removed, and the checks 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 check, 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 check, about the thirty-second part of an inch below the level of the inside check, 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 Mediaeval 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 CCLXXV., 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.
Glass. 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 chink, 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 manipulative 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 a. 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. coloured 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 servitor, the third the foot-maker, 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 marrer, as in fig. 7, until it has acquired the circular shape seen there. The marrer 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 vacuity, 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 dropped 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 incased 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
Glass. 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 sifting 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.
W. C—R. AND J. B.