INK

INK, a black liquor used in writing, generally made of an infusion of galls, copperas, and gum-arabic.

The properties which this liquid ought to have, are, 1. To flow freely from the pen, and sink a little into the paper, that the writing be not easily discharged. 2. A very deep black colour, which should be as deep at first as at any time afterwards. 3. Durability, so that the writing may not be subject to decay by age. 4. Ink should be destitute of any corrosive quality, that it may not destroy the paper, or go through it in such a manner as to render the writing illegible. No kind of ink, however, hath yet appeared which is possessed of all these qualities. The ink used by the ancients was possessed of the second, third, and fourth qualities above-mentioned, but wanted the first. Dr Lewis hath discovered its composition from some passages in ancient authors. "Pliny and Vitruvius, (says he), expressly mention the preparation of foot, or what we now call lamp-black, and the composition of writing-ink from lamp-black and gum. Dioscorides is more particular, setting down the proportions of the two ingredients, viz. three ounces of the foot to one of the gum. It seems the mixture was formed into cakes or rolls; which being dried in the sun, were occasionally tempered with water, as the cakes of Indian ink are among us for painting."

In Mr Delaval's Treatise on Colours, p. 37, he acquaints us, that with an infusion of galls and iron filings, he had not only made an exceedingly black and durable ink, but by its means, without the addition of any acid, dyed silk and woollen cloth of a good and lasting black. This kind of ink, however, tho' the colour is far superior to that of any other, hath the inconvenience of being very easily discharged, either by the smallest quantity of any acid, or even by simple water; because it doth not penetrate the paper in such a manner as is necessary to preserve it from the instantaneous action of the acid or of the water. During the action of the infusion of galls upon the iron in making this kind of ink, a very considerable effervescence takes place, and a quantity of air is discharged, the nature of which hath not yet been examined.

The materials usually employed for the making of ink are, common green vitriol, or copperas, and galls; but almost all of them are deficient in durability, which is a property of such importance, that Dr Lewis hath thought the subject of ink-making not unworthy of his attention. From experiments made by that author, he infers, that the decay of inks is chiefly owing to a deficiency of galls; that the galls are the most perfu-

able ingredient, the quantity of these, which gives the greatest blackness at first, (which is about equal parts with the vitriol), being insufficient to maintain the colour: that for a durable ink, the quantity of galls cannot be much less than three times that of the vitriol; that it cannot be much greater, without lessening the blackness of the ink: that by diminishing the quantity of water, the ink was rendered blacker and more durable; that distilled water, rain water, and hard spring-water, had the same effects: that white-wine produced a deeper black colour than water; that the colour produced by vinegar was deeper than that by wine; that proof-spirit extracted only a reddish brown tinge: that the last-mentioned tincture sunk into, and spread upon, the paper; and hence the impropriety of adding spirit of wine to ink, as is frequently directed, to prevent mouldiness or freezing: that other astringents, as oak-bark, bilwort, sloe-bark, &c. were not so effectual as galls, nor gave so good a black, the colour produced by most of these, excepting oak-bark, being greenish: that the juice of sloes did not produce a black colour with martial vitriol; but that, nevertheless, the writing made with it became black, and was found to be more durable than common ink: that inks made with saturated solutions of iron in nitrous, marine, or acetic acids, in tartar, or in lemon-juice, were much inferior to the ink made with martial vitriol: that the colour of ink was depraved by adding quicklime, which was done with an intention of destroying any superabundant acid which might be supposed to be the cause of the loss of the colour of ink: that the best method of preventing the effects of this superabundant acid is probably by adding pieces of iron to engage it; and that this conjecture was confirmed by an instance the author had heard, of the great durability of the colour of an ink in which pieces of iron had been long immersed: and lastly, that a decoction of logwood used instead of water, sensibly improved both the beauty and deepness of the black, without disposing it to fade. The same author observes, that the addition of gum-arabic is not only useful, by keeping the colouring matter suspended in the fluid, but also by preventing the ink from spreading, by which means a greater quantity of it is collected on each stroke of the pen. Sugar, which is sometimes added to ink, was found to be much less effectual than gums, and to have the inconvenience of preventing the drying of the ink. The colour of ink is found to be greatly injured by keeping the ink in vessels made of copper or of lead, and probably of any other metal, excepting iron, which the vitriolic acid can dissolve.

The foregoing experiments point out for the best proportions of the ingredients for ink, One part of green vitriol, one part of powdered logwood, and three parts of powdered galls. The best menstruum appears to be vinegar or white-wine, though for common use water is sufficient. If the ink be required to be of a full colour, a quart, or at most three pints, of liquor, may be allowed to three ounces of galls, and to one ounce of each of the other two ingredients. Half an ounce of gum may be added to each pint of the liquor. The ingredients may be all put together at once in a convenient vessel, and well shaken four or five times each day. In 10 or 12 days the ink will be fit for use, though it will improve by

remaining longer on the ingredients. Or it may be made more expeditiously, by adding the gum and vitriol to a decoction of galls and logwood in the menstruum. To the ink, after it has been separated from the feculencies, some coarse powder of galls, from which the fine dust has been sifted, together with one or two pieces of iron, may be added, by which its durability will be secured.

In some attempts made by the Doctor to endow writing ink with the great durability of that of the ancients, as well as the properties which it hath at present, he first thought of using animal-glues, and then of oily matters. "I mixed both lamp-black (says he) and ivory-black with solution of gum arabic, made of such consistence as just to flow sufficiently from the pen. The liquors wrote of a fine black colour; but when dry, part of the colour could be rubbed off, especially in moist weather, and a pencil dipped in water washed it away entirely.

"I tried solutions of the animal-glues, with the same event. If glafs or fish-glue being the most difficultly dissoluble of these kinds of bodies, I made a decoction of it in water, of such strength, that the liquor concreted into a jelly before it was quite cold: with this jelly, kept fluid by sufficient heat, I mixed some ivory-black: characters drawn with this mixture on paper bore rubbing much better than the others, but were discharged without much difficulty by a wet pencil.

"It was now suspected, that the colour could not be sufficiently fixed on paper without an oily cement. As oils themselves are made miscible with watery fluids by the intervention of gum, I mixed some of the softer printers varnish, after-mentioned, with about half its weight of a thick mucilage of gum arabic, working them well together in a mortar, till they united into a smooth uniform mass: this was beaten with lamp-black, and some water added by little and little, the rubbing being continued till the mixture was diluted to a due consistence for writing. It wrote freely, and of a full brownish-black colour: the characters could not be discharged by rubbing, but water washed them out, though not near so readily as any of the foregoing. Instead of the printers varnish or boiled oil, I mixed raw linseed oil in the same manner with mucilage and lamp-black; and on diluting the mixture with water, obtained an ink not greatly different from the other.

"Though these oily mixtures answered better than those with simple gums or glues, it was apprehended that their being dischargeable by water would render them unfit for the purposes intended. The only way of obviating this imperfection appeared to be, by using a paper which should admit the black liquid to sink a little into its substance. Accordingly I took some of the more sinking kinds of paper, and common paper made damp as for printing; and had the satisfaction to find, that neither the oily nor the simple gummy mixtures spread upon them so much as might have been expected, and that the characters were as fixed as could be desired, for they could not be washed out without rubbing off part of the substance of the paper itself.

"All these inks must be now and then stirred or shaken during the time of use, to mix up the black powder, which settles by degrees to the bottom: those

with oil must be well shaken also, though not used, once a-day, or at least once in three or four days, to keep the oil united with the water and gum; for if once the oil separates, which it is apt to do by standing at rest for some days, it can no longer be mixed with the thin fluid by any agitation. But though this imperfect union of the ingredients renders these inks less fit for general use than those commonly employed, I apprehend there are many occasions in which these kinds of inconveniences will not be thought to counterbalance the advantage of having writings which we may be assured will be as lasting as the paper they are written upon. And indeed the inconvenience may be in a great measure obviated by using cotton in the ink-stand, which, imbibing the fluid, prevents the separation of the black powder diffused through it.

"All the inks, however, made on the principle we are now speaking of, can be discharged by washing, unless the paper admits them to sink into its substance. The ancients were not insensible of this imperfection; and sometimes endeavoured to obviate it, according to Pliny, by using vinegar, instead of water, for tempering the mixture of lamp-black and gum. I tried vinegar, and found it to be of some advantage, not as giving any improvement to the cement, but by promoting the sinking of the matter into the paper. As this washing out of the ink may be prevented, by using a kind of paper easy enough to be procured, it is scarcely to be considered as an imperfection; and indeed, on other kinds of paper, it is an imperfection only so far as it may give occasion to fraud, for none of these inks are in danger of being otherwise discharged than by design. The vitriolic inks themselves, and those of printed books and copperplates, are all dischargeable; nor can it be expected of the ink-maker to render writings secure from frauds.

"But a further improvement may yet be made, namely, that of uniting the ancient and modern inks together; or using the common vitriolic ink instead of water, for tempering the ancient mixture of gum and lamp-black. By this method it should seem that the writings would have all the durability of those of former times, with all the advantage that results from the vitriolic ink fixing itself in the paper. Even where the common vitriolic mixture is depended on for the ink, it may in many cases be improved by a small addition of the ancient composition, or of the common Indian ink which answers the same purpose: when the vitriolic ink is dilute, and flows so pale from the pen, that the fine strokes, on first writing, are scarcely visible, the addition of a little Indian ink is the readiest means of giving it the due blackness. By this admixture it may be presumed also that the vitriolic ink will be made more durable, the Indian ink in some measure covering it, and defending it from the action of the air. In all cases, where Indian ink or other similar compositions are employed, cotton should be used in the ink-stand, as already mentioned, to prevent the settling of the black powder."

Indian Ink, a valuable black for water-colours, brought from China and other parts of the East Indies, sometimes in large rolls, but more commonly in small quadrangular cakes, and generally marked with Chinese characters. Dr Lewis, from experiments made on this substance, hath shewn that it is composed

of fine lamp-black and animal-glue: and accordingly, for the preparation of it, he desires us to mix the lamp-black with as much melted glue as is sufficient to give it a tenacity proper for being made into cakes; and these when dry, he tells us, answered as well as those imported from the East Indies, both with regard to the colour, and the freedom of working. Ivory-black, and other charcoal-blacks, levigated to a great degree of fineness, answered as well as the lamp-black; but in the state in which ivory-black is commonly sold, it proved much too gritty, and separated too hastily from the water.

Printing Ink, is totally different from Indian ink, or that made use of in writing. It is an oily composition, of the consistency of an ointment: the method of preparing it was long kept a secret by those whose employment it was to make it, and who were interested in concealing it; and even yet is but imperfectly known. The properties of good printing-ink are, to work clean and easily, without daubing the types, or tearing the paper; to have a fine black colour; to wash easily off the types; to dry soon; and to preserve its colour, without turning brown. This last, which is a most necessary property, is effectually obtained by setting fire to the oil with which the printing ink is made for a few moments, and then extinguishing it by covering the vessel (A). It is made to wash easily off the types, by using soap as an ingredient; and its working clean depends on its having a proper degree of strength, which is given by a certain addition of rosin. A good deal, however, depends on the proportion of the ingredients to each other; for if too much soap is added, the ink will work very foul, and daub the types to a great degree. The same thing will happen from using too much black, at the same time that both the soap and black hinder the ink from drying; while too much oil and rosin tear the paper, and hinder it from washing off.—The following receipt has been found to make printing ink of a tolerable good quality. "Take a Scots pint of linseed oil, and set it over a pretty brisk fire in an iron or copper vessel capable of holding three or four times as much. When it boils strongly, and emits a thick smoke, kindle it with a piece of paper, and immediately take the vessel off the fire. Let the oil burn for about a minute; then extinguish it by covering the vessel; after it has grown pretty cool, add two pounds of black rosin, and one pound of hard soap cut into thin slices. If the oil is very hot when the soap is added, almost the whole mixture will run over the vessel. The mixture is then to be set again over the fire; and when the ingredients are thoroughly melted, a pound of lamp-black, previously put through a lawn sieve, is to be stirred into it. The whole ought then to be ground on a marble stone, or in a mill like the levigating mill described under the article CHEMISTRY, n^o 97."

Though the above receipt is greatly superior to any that hath been hitherto published, all of which are capitally deficient in not mentioning the necessary ingredients of rosin and soap; yet it must be acknowledged, that ink made in this manner is inferior in point of colour, and is likewise more apt to daub the types and make an indistinct impression, than such

as is prepared by some of those who make the manufacture of this commodity their employment; so that either a variation in the proportion of the ingredients, a nicety in the mixture, or some additional ingredient, seems necessary to bring it to the requisite perfection.

Ink for the Rolling Press, is made of linseed oil burnt in the same manner as that for common printing-ink, and then mixed with Francefort-black, and finely ground. There are no certain proportions which can be determined in this kind of ink; every workman adding oil or black to his ink, as he thinks proper, in order to make it suit his own taste.—Some, however, mix a portion of common boiled oil which has never been burnt: but this must necessarily be a bad practice, as such oil is apt to go through the paper; a fault very common in prints, especially if the paper is not very thick. No soap is added; because the ink is not cleared off from the copperplates with alkaline ley as in common printing, but with a brush dipped in oil.

Ink is also an appellation given to any coloured liquor used in writing, whether red, yellow, green, &c. Many different kinds of these inks may be prepared by the directions given under the article COLOUR-MAKING, which it would be superfluous here to repeat.

Sympathetic Ink, a liquor with which a person may write, and yet nothing appear on the paper after it is dry, till some other means are used, such as holding the paper to the fire, rubbing it over with some other liquor, &c.

These kinds of ink may be divided into seven classes, and that with respect to the means used to make them visible; viz. 1. Such as become invisible by passing another liquor over them, or by exposing them to the vapour of that liquor. 2. Those that do not appear so long as they are kept close, but soon become visible on being exposed to the air. 3. Such as appear by strewing or lifting some very fine powder of any colour over them. 4. Those which become visible by being exposed to the fire. 5. Such as become visible by heat, but disappear again by cold or the moisture of the air. 6. Those which become visible by being wetted with water. 7. Such as appear of various colours, red, yellow, blue, &c.

I. The first class contains four kinds of ink, viz. solutions of lead, bismuth, gold, and green vitriol. The first two become visible in the same manner, viz. by the contact of sulphureous liquids or fumes. For the first, a solution of common sugar-of-lead in water will answer as well as more troublesome preparations. If you write with this solution with a clean pen, the writing when dry will be totally invisible: but if it be wetted with a solution of hepar sulphuris, or of orpiment, dissolved by means of quick-lime; or if it be exposed to the strong vapours of these solutions, but especially to the vapour of volatile tincture of sulphur; the writing will appear of a brown colour, more or less deep according to the strength of the sulphureous fume. By the same means, what is wrote with the solution of bismuth in spirit of nitre will appear of a deep black.

The sympathetic ink prepared from gold, depends on

Ink. on the property by which metal precipitates from its solvent on the addition of a solution of tin. If you write with a solution of gold in aqua regia, and let the paper dry gently in the shade, nothing will appear for the first seven or eight hours. Dip a pencil or a small fine sponge in the solution of tin, and drawing it lightly over the invisible characters, they will immediately appear, of a purple colour.

Characters wrote with a solution of green vitriol carefully depurated, will likewise be invisible when the paper is dry; but if wetted with an infusion of galls, they will immediately appear as if wrote with common ink. If, instead of this infusion, a solution of the phlogisticated alkali, impregnated with the colouring matter Prussian blue is made up of, the writing will appear of a very deep blue.

II. To the second class belong the solutions of all those metals which are apt to attract phlogiston from the air, such as lead, bismuth, silver, &c. The sympathetic ink of gold already mentioned belongs also to this class; for if the characters wrote with it are long exposed to the air, they become by degrees of a deep violet colour, nearly approaching to black. In like manner, characters wrote with a solution of silver in aqua fortis are invisible when newly dried, but being exposed to the sun, appear of a grey colour like slate. To this class also belong solutions of lead in vinegar; copper in aqua fortis; tin in aqua regia; emery, and some kinds of pyrites, in spirit of salt; mercury, in aqua fortis; or iron, in vinegar. Each of these has a particular colour when exposed to the air; but they have the disagreeable property of corroding the paper, so that after some time the characters appear like holes cut out of the paper.

III. The third class of sympathetic inks contains such liquids as have some kind of glutinous viscosity, and at the same time are long a drying; by which means, though the eye cannot discern the characters wrote with them upon paper, the powders strewed upon them immediately adhere, and thus make the writing become visible. Of this kind are urine, milk, the juices of some vegetables, weak solutions of the deliquescent salts, &c.

IV. This class, comprehending all those that become visible by being exposed to the fire, is very extensive, as it contains all those colourless liquids in which the matter dissolved is capable of being reduced, or of reducing the paper, into a sort of charcoal by a small heat. A very easily procured ink of this kind is oil of vitriol diluted with as much water as will prevent it from corroding the paper. Letters wrote with this fluid are perfectly invisible when dry, but instantly appear as black as if wrote with the finest ink on being held near the fire. Juice of lemons or onions, a solution of sal-ammoniac, green vitriol, &c. will answer the same purpose, though not so easily, or with so little heat.

V. The fifth class comprehends only solutions of Regulus of Cobalt in spirit of salt; for the properties of which, see CHEMISTRY, n^o 259.

VI. This class comprehends such inks as become visible when characters wrote with them are wetted with water. They are made of all such substances as deposit a copious sediment when mixed with water, dissolving only imperfectly in that fluid. Of this kind

are dried alum, sugar-of-lead, vitriol, &c. We have therefore only to write with a strong solution of these salts upon paper, and the characters will be invisible when dry; but when we apply water, the small portion of dried salt cannot again be dissolved in the water. Hence the insoluble part becomes visible on the paper, and shews the characters wrote in white, grey, brown, or any other colour which the precipitate assumes.

VII. Characters may be made to appear of a fine crimson, purple, or yellow, by writing on paper with solution of tin in aqua regia, and then passing over it a pencil dipped in a decoction of cochineal, Brazil-wood, logwood, yellow-wood, &c.—For an account of the nature of all these sympathetic inks, however, and the principles on which they are made, see the articles CHEMISTRY and COLOUR-MAKING, passim.