INK, a black liquor, used in writing. The name is also applied to liquids and pigments of various colours, used in printing as well as in writing. We shall notice these compounds in the following order, 1. Black Writing Ink, comprehending under this head the ordinary methods of composition recommended by chemists, the improvements which a more extended manufacture have effected, the methods suggested for rendering ink imperishable, and the inquiries which have been instituted into the composition of ancient inks, with the methods proposed for renewing faded writing; 2. Indian Pigment or Ink; 3. Red Ink; 4. Blue Ink; 5. Printing Ink; 6. Ink for the Rolling Press; 7. Lithographic Ink; 8. Sympathetic Ink.

Black Writing Ink. The properties which this liquor ought to have, are, 1. To flow freely from the pen, and sink a little into the paper, that the writing may not be 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; and 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.

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 addition of any acid, dyed silk and woollen cloth of a good and lasting black. This kind of ink, however, though the colour is far superior to that of any other, has the inconvenience of being very easily discharged, either by the smallest quantity of any acid, or even by simple water; because it does 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 has 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 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 perishable ingredient, the quantity of these, which gives the greatest blackness at first (that is, about equal parts with the vitrioD, 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 is rendered blacker and more durable; that distilled water, rain-water, and hard spring-water, have the same effects; that white wine produces a deeper black colour than water; that the colour produced by vinegar is deeper than that by wine; that proof-spirit extracts only a reddish brown tinge; that the last-mentioned tincture sinks into, and spreads 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, bistort, sloe-bark, &c. are not so effectual as galls, nor give so good a black, the colour produced by most of these, excepting oak-bark, being greenish; that the juice of sloes does not produce a black colour with martial vitriol; but that, nevertheless, the writing made with it becomes black, and is found to be more durable than common ink: that inks made with saturated solutions of iron, in nitrous, marine, or acetous acids, in tartar, or in lemon juice, were much inferior to the ink made with martial vitriol; that the colour of ink is depraved by adding quicklime, which is done with an intention of destroying any superabundant acid which may 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; that this conjecture is 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 improves 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, is 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, which the vitriolic acid can dissolve.

The foregoing experiments point out 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 ten or twelve days the ink will be fit for use, though it will improve by remaining longer on the in-gredients[7:12:278]. 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.

Such is the substance of the discoveries and inquiries made by Dr Lewis and other chemists, relative to the composition of black writing ink, and upon modifications of them, most of the methods hitherto followed in making it have been founded. It might be supposed that after the determination, by such authority, of the relative proportions of the usual ingredients, it would only have been necessary to attend to that proportion, and that the result would be uniformly satisfactory. Experience, however, has shewn the reverse of this; and it is often found that the same ingredients, and the same proportions of them, produce inks of very different qualities. This arises from two causes, which were not apparent to the expèrimenting chemist. His attention was chiefly directed to the immediate effect produced by the mixture he prepared, or the additions made to it. Hence his experiments generally led him to the formation of a good black dye, if applied to immediate use; whilst the ultimate effect of the action of the atmosphere on the liquid itself, and the decomposition which frequently resulted, from the quantity of vegetable matter contained in it, were seldom brought under his notice. To these two causes, as well as the various modes of extract and of mixture, are to be attributed the very different results which have arisen from the use of the same ingredients and the same proportions of them; and on the connexion and regulation of these two agents, we believe the quality of the ink to depend, as much as upon the nature and proportion of the materials employed. This opinion is strengthened by the information we have received from Mr Morison (the extent of whose ink manufactories is a remarkable instance of the importance of the most minute branch of the arts, at the present day, in Great Britain), who has assured us, that he never could depend on the quality of the ink which was to be produced from any mixture of ingredients, however well manipulated, or however’strong, until he adopted a method of abstracting that part of the vegetable ingredients which induced decomposition; a process which required much time and attention, but in the accomplishment of which so full opportunity was given for the action of the atmosphere that the liquid was not liable to be afterwards affected by either cause.

In some attempts made by Dr Lewis to endow writing ink with the great durability of that of the ancients, as well as the properties which it has 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 solutions 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. Isinglass 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 fixed some of the softer painters’ 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 painters’ 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.

“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, to prevent the settling of the black powder.”

There is little doubt that the monkish ink was a composition of this nature, combining in some degree the ancient and modern materials. The ancient ink must have been very similar to the Indian or Chinese cakes. Pliny and Vitruvius both mention it as a preparation of soot, or lamp-black, with glue or gum; and Dioscorides gives the proportions of three parts of soot to one of gum. To this the liquor extracted from the cuttle-fish had sometimes been added. When this could not be had, there is indeed great reason to believe that some of the modern vitriolic ingredients were added by the ancients; many of the manuscripts of the Greek and Roman authors, erased by the monks, having been found to retain as much of the vitriolic principle as to become again legible on the application of chemical tests.

In the Philosophical Transactions for 1787, DrBlagden gives some account of a method of restoring decayed inks so as to render them legible. His experiments originated from a conversation with Mr Astle, on the question whether the inks made eight or ten centuries ago, and which are found to have preserved their colour very well, were made of the same ’materials now employed or not? In order to decide the question, Mr Astle furnished the doctor with several manuscripts on parchment and vellum from the ninth [7:12:279]to the fifteenth centuries inclusively. Some of these were still very blaok; others of different shades, from a deep yellowish brown to a very pale yellow, in some parts so faint that it could scarcely be seen. This was tried with simple and phlogisticated alkalies, the mineral acids, and infusion of galls. From these experiments it appeared that the ink anciently employed was of the same nature as at present. The letters turned of a reddish or yellowish brown, with alkalies became pale, and were at length obliterated by the diluted mineral acids. The drop of acid liquor, which had been put upon a letter, changed to a deep blue or green on the addition of phlogisticated alkalies; with an infusion of galls, in some cases the letters acquired a deep tinge, in others a slight one. “Hence,” says the doctor, “it is evident that one of the ingredients was iron, which there is no reason to doubt was joined with the vitriolic acid; and the colour of the more perfect manuscripts, which in some was a deep black, and in others a purplish black, together with the restitution of that colour in those which had lost it by the infusion of galls, sufficiently proved that another of the ingredients was astringent matter, which from history appears to have been that of galls. No trace of a black pigment of any sort was discovered; the drop of acid, which had completely extracted a letter, appearing of an uniform pale and ferruginous colour, without an atom of black powder, or other extraneous matter, floating in it.”

In considering the methods of restoring the legibility of decayed writings, our author observes, that perhaps one of the best may be to join phlogisticated alkali with the calx of iron which remains; because the precipitate formed by these two substances greatly exceeds that of the iron alone. On this subject Dr Blagden disagrees with Mr Bergmann; but to bring the matter to a test, the following experiments were made.

1. The phlogisticated alkali was rubbed in different quantities upon the bare writing. This, in general, produced little effect, though, in a few instances, it gave a bluish tinge to the letters, and increased their intensity; “probably,” says the doctor, “where something of an acid nature had contributed to the diminution of their colour.” 2. By adding, besides the alkali, a diluted mineral acid to the writing, our author found his expectations fully answered; the letters then changing quickly to a very deep and beautiful blue. It is but of little consequence whether the acid or phlogisticated alkali be first added; though upon further consideration the doctor inclined to begin with the alkali. The reason is, that when the alkali is first put on, the colour seems to spread less, and thus not to hurt the legibility of the writing so much as would otherwise be done. His method is to spread the alkali thin over the writing with a feather, then to touch it as gently as possible upon or nearly over the letters with the diluted acid by means of a feather or bit of stick cut to a blunt point. The moment that the acid liquor is applied, the letters turn to a fine blue, beyond comparison stronger than the original trace of the letter; and by applying a bit of blotting-paper to absorb the superfluous liquid, we may in a great measure avoid the staining of the parchment; for it is this superfluous liquor which, absorbing part of the colouring matter from the letters, becomes a dye to whatever it touches. Care ought, however, to be taken not to allow the blotting-paper to come in contact with the letters, because the colouring matter may easily be rubbed off while soft and wet. Any one of the three mineral acids will answer the purpose effectually. Dr Blagden commonly uses the marine. But whichever of the three is used, it ought to be diluted so far as not to be in danger of corroding the parchment; after which the degree of strength seems not to be a matter of great nicety.

Another method of restoring the legibility of old writings is by wetting them with an infusion of galls in white wine; but this is subject to the same inconvenience with the former, and is besides less efficacious. The doctor is of opinion that the acid of the galls by itself would be better for the purpose than the infusion of the whole substance of them; and he thinks also that a preferable kind of phlogisticated alkali might be prepared either by purifying the common kind from iron as much as possible, or by making use of the volatile alkali instead of the fixed. Mr Astle mentions a method of restoring the legibility of decayed writings; but says that it ought not to be hazarded, lest a suspicion of deceit should arise.

The illegibility of modern manuscripts, compared with those of an earlier date, is a matter of much interest, and has of late excited considerable inquiry. It appears to us, that the greater durability of the colour of the ink in old manuscripts is owing not only to the strength of the ink, but to the quality of the paper and vellum. The strength of the astringent or tannin principle is acknowledged on all hands to be that on which the durability of a vitriolic ink chiefly depends. Now that principle is strong not only in old vellum, but it is retained to a considerable extent in old paper made from linen rags. The vellum formerly used was prepared by a tedious process, by which tannin was largely imparted to it in the same manner as to leather; and to this cause old vellum owes its deep brown colour more than to mere age. In like manner, the paper, instead of being bleached, as is now done, with oxymuriatic acid, to bring up the colour, as it is called, but, in fact, to destroy the natural colour of the paper, and to deprive it of one of its most valuable qualities, was allowed to retain somewhat of its original flax colour, and with its colour a large proportion of the astringent quality on which the tenuity of the paper, as well as its preservative property, depended. On that strong vellum, parchment, and paper, our ancestors wrote with an ink, the component parts of which seem to have been the same as of that now in use; but as they wrote more seldom, and were not in so great haste, as their descendants, they were content to use their ink so thick, that the quantity of gum in it was sufficient to hold a very strong mixture of the other ingredients in suspension. This superabundance of gum or glue was not only serviceable in this respect, but it also acted as a varnish, defending the ink from the corrosive action of the atmosphere. Nor were these the only precautions taken. It will be observed, that those writings on vellum which are in the best preservation, are not only of a deep brown shade, and the ink with an apparent body of colour, but the grain side of the vellum, or that not written upon, is smooth, almost as if it had been burnished. This seems to have been done with animal glue, and afterwards well rubbed. The ink was thus not only preserved from the action of the air on the one side by the varnish incorporated with it, but protected on the other by the polished surface of the parchment.

Taking these circumstances into consideration, and giving them their due weight, we feel convinced that any effectual plan for giving durability to the public records of the kingdom or other deeds of importance, must commence with the improvement of the paper and vellum upon which they are written. This is a matter deserving the attention of government, and the correction of which is within its reach. The books of records kept in the public offices are or ought to be under its superintendence; and the only deeds the preservation of which is of importance are written upon stamped paper, the issue of which is also within the control of the government. By offering premiums for the manufacture of paper in which the tannin or astringent principle is most effectually preserved or introduced, and using proper precautions respecting the ink with which the deeds are written, we can see nothing in the nature or composition [7:12:280]of either to prevent us securing at the very least as great a degree of durability as pertains to the early records of the kingdom.

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, has 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.

Red Ink. The red ink in common use for writing or ruling is a decoction of Brazil wood in vinegar, the colour of which is raised by alum. It answers every ordinary {>urpose of business, but the colour is evanescent, especial-y on highly bleached paper, the oxymuriatic acid in which turns the ink first of a purple colour and then gradually whitens it. No red ink which will stand exposure to the air has yet been discovered, save a thin pigment of vermilion, with which many old bibles were ruled; but it can easily be washed off.

Blue Ink. The dye commonly called liquid blue is frequently used for writing, being, if well made, durable; and when diluted with water forms the ink with which the e ∕⅛⅛∕ lines in ruling are drawn. It îs made of indigo dissolved in sulphuric acid, the strength of the acid being afterwards reduced by throwing into the liquid mass pieces of chalk or of an alkali.

For other coloured inks see Colour Making. Printing Ink, is totally different from Indian ink, or that made use of in writing. It is an oily composition, of the consistence 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 it 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.^[1. This is mentioned by Dr Lewis in his Philosophical Commerce of Arts ; but he seems not to have been acquainted with the method of giving it the other necessary properties. ] 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 greater 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; whilst 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 Scotch 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 levigating milk

Though the above receipt is greatly superior to any that has 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 burned in the same manner as that for common printing ink, and then mixed with Francfort-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 burned; 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.

Lithographic Ink. The ink used for writing or drawing in lithography is described under that article. For printing ink to be used in lithography, prepare a varnish or varnishes, of various degrees of tenuity, by boiling and burning old linseed oil in an iron pot with a closely fitting metal cover. When the varnish is of the thickness required, throw in some pieces of stale bread to absorb the fatty matter. Into this varnish, when cold, grind lamp-black or Francfort-black, adding a little indigo and rose-pink, which give depth to the black. It must be ground until so fine that no particles are observed on turning it over with a palette knife. For blue, use indigo; for red, vermilion.

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

These kinds of ink may be divided into seven classes, with respect to the means used to make them visible, viz. 1. such as become visible 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 sifting 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; and, 7∙ such as appear of various colours.

The first class contains four kinds of ink, viz. solutions of lead, bismuth, gold, and green vitriol, or sulphate of iron. The two first become visible by the contact of sulphureous liquids or fumes. For the first, a solution of common sugar of lead in water answers very well. With this solution write with a clean pen, and the writing when dry will be totally invisible; but if it be wetted with a solution of [7:12:281]hepar sutpiiuτιs i or of orpiment, dissolved by means of quicklime, or exposed to the strong vapours of these solutions, the writing will appear of a brown colour, more or Jess deep, according to the strength of the sulphureous fume. By the same means the solution of nitrate of bismuth will appear of a deep black.

The sympathetic ink prepared from gold depends on the property by which that metal precipitates from its solvent on the addition of a solution of tin. Write with a solution of gold in nitro-muriatic acid, and let the paper dry gently in the shade; nothing will appear for the first seven or eight hours. Dip a pencil in the solution of tin, and draw it lightly over the invisible characters, they will immediately appear, of a purple colour.

Characters written with a solution of green vitriol will likewise be invisible when the paper is dry; but if wetted with an infusion of galls, they will immediately appear as if written with common ink. If, instead of this infusion, a solution of an alkaline prussiate be used, the writing will appear of a deep blue.

To the second class belong the solutions of all those metals which are apt to attract oxygen 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 written 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 written with a solution of nitrate of silver are invisible when newly dried, but being exposed to the sun, appear of a gray colour like slate. To this class also belong solutions of sugar of lead, nitrates of copper and of mercury, acetate of iron, and muriate of tin. Each of these has a particular colour when exposed to the air; but they corrode the paper.

The third class of sympathetic inks contains such liquids as have some kind of glutinous viscosity, and at the same time are long in drying; by which means, though the eye cannot discern the characters written 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, and other liquids.

The fourth 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, and of reducing the paper into a sort of charcoal by a small heat. Sulphuric acid, diluted with as much water as will prevent it from corroding the paper, makes a good ink of this kind. Letters written with this fluid arc invisible when dry, but instantly on being held near the fire appear as black as if written with the finest ink. Juice of lemons or onions, a solution of sal ammoniac, green vitriol, &c. answer the same purpose.

The fifth class comprehends only a solution of muriate of cobalt.

Ί he sixth class comprehends such inks as become visible when characters written 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, and other substances. 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 written in white, gray, brown, or any other colour which the precipitate assumes.

Lastly, characters may be made to appear of a fine crimson, purple, or yellow, by writing on paper with solution of muriate of tin, and then passing over it a pencil dipt in a decoction of cochineal, Brazil-wood, log-wood, yellowwood, or the like.

A treatise upon inks was published by Peter Caniparius, professor of Medicine at Venice, of which an edition was printed at London in 1660. It is divided into six parts. The first treats of inks made from pyrites, stones, and metals; the second of such as are made from metals and calces; the third of those which are prepared from soots and vitriols; the fourth of the different kinds of inks used by the librarii or book-writers, by printers, and engravers: likewise of staining or writing upon marble, stucco, or sea-gliolia, and of encaustic modes of writing; of liquids for painting or colouring leather and linen or woollen cloth, and of restoring inks that had been decayed by time; together with many methods of effacing writing, restoring decayed paper, and different modes of secret writing. The fifth treats of writing inks made in different countries from gums, woods, the juices of plants, and the like, as well as of different kinds of varnishes. The sixth treats of the different methods of extracting vitriol, and the chemical uses of it.

Weckerus, in a treatise de Secretis, printed at Basil in 1612, contains a number of curious particulars concerning ink. He also gives receipts for making gold and silver inks, composed both with these metals and without them; and directions for making inks for secret writing, and for effacing them, though in this last part there are many particulars bordering too much on the marvellous.

Ink Stones, a kind of small round stones, of a white, red, gray, yellow, or black colour, containing a quantity of native martial vitriol, from which they derive the property of making ink, and hence their name. They are almost entirely soluble in water, and besides their other ingredients, contain also a portion of copper and zinc.