« AnteriorContinuar »
without materially fading or becoming illegible, dries very soon after writing with it, and does not considerably ■ corrode or soften the pen. The basis of all the common writing inks is the fine black, or dark blue precipitate, formed by the addition of vegetable astringents, and particularly the soluble part of the call nut, to a solution of iron, generally the sulphate. Bnt as this, if diffused in water alone, would subside in a short time, and leave the supernatant liquor nearly without colour, the precipitate is kept suspended, by thickening the water with gum arabic, or any other gum mucilage, which also gives the ink the due consistence, and enables it to trace a fine stroke on the paper, without running. These materials, therefore, that is, gall-nuts, green vitriol, (sulphate of iron) gum arabic, and water, are all that are necessary for the composition of ink; and if they are of good quality, and properly proportioned to each other, every other addition usually made adds very little to its perfection.
It is not well ascertained how soon the present kind of writing ink came into use. It has certainly been employed for many centuries in most European countries; but the ancient Roman inks were, for the most part, of a totally different composition, being made of some vegetable carbonaceous matter like lamp-black diffused in a liquor. The Chinese, and many of the inks used by the Oriental nations, are still of this kind.
On the subject of the common writing ink, Dr. Lewis (" Commerce of Arts") has so full and so accurate an investigation, and his experiments are so simple and well devised, that little else can be added to the subject in a technical point of view. For a fuller chemical inquiry into the nature of the atramentous precipitate, the reader is referred to the articles Gallic Acid and Iron.
Dr. Lewis first endeavoured to ascertain the best proportion between the galls and the sulphate of iron, to render the ink permanent; for it is to be observed, that with almost any proportions, if the entire quantity be sufficient, the ink will be fine and black at first, but many of these inks if kept for some time, especially exposed to light and air, will grow brown and fade, and the letters made with it will become nearly illegible.
By trying different proportions of galls and sulphate of iron, it was found, that when about in equal quantities (the galls being
powdered, and boiled fully to extract tlaesr soluble parts) they appeared to be ratarnaDy saturated, so that the mixed liquors wool.. receive no additional blackness, from a anther dose of one or the other.
This, however, was only a rough atrpsnrzimation to accuracy, for the same effect was> produced when either substance n> atftse in a small degree superior in quantity to the other. But Dr. Lewis found that an ink, with equal parts of the two, thonet very black at first, changed to a yeUowxssa brown, upon exposure to the sun and air only for a few days. This was again blackened by washing with fresh pall infosjoa. and hence it appears in fair inference q*»* the calls are a perishable substance, so that to insure durability, a much greater proportion must enter into the ink than is required for mere saturation in the first in stance. Thus it was found that two parts of galls and one of vitriol, make a much more durable ink than with equal parts, and three of galls with one of vitriol was still more durable. When the galls were increased beyond this point, the colon? was indeed quite permanent, but it wa not of so full a black.
The proportion of water or other liquid to the solid ingredients, will admit of great variation. One part of vitriol, three of calls, and fifty parts of water, gave as ink black enough for common use, but the finest and blackest was made when only ten of water were employed; nor was any deficiency in the gallic acid observed after fifteen years, though the water was scarcely more than sufficient to cover the galls, and therefore could hardly be supposed capable of extracting all the soluble part of them; and though the vitriol from its greater solubility would probably be dissolved entirely, and thus be in greater proportion than usual. Other liquors besides water were tried. Of these, white wine and vinegar appeared to answer somewhat better; but any considerable proportion of spirit of wine, or brandy, obviously did harm, owing to the insolubility of the sulphate of iron (as of all the other sulphates) in alcohol, and therefore its diminished solubility in any liquor is in proportion to the alcohol it contains. A decoction of logwood used instead of water sensibly improved the beauty of the colour.
Instead of galls other astringents were employed, such as sloes, oak-bark, tonnentil root, &C. ; but though they all gave I good blue black, with the salt of iron, none
of tbem was equal to the gall-nut in this reaped.
Other salts of iron were also substitated to the sulphate. The muriate and nitrate of iron nearly equalled the sulphate in colour, but proved too corrosive to the paper, and as they were in no respect preferable to the sulphate, there is no reason for abandoning it.
Imagining that there must be some excels of sulphuric acid in common ink, to which the fading might be imputed, Dr. Lewis tried to neutralize it by lime and alkalies, but with manifest injury, the colour being rendered thereby extremely fugitive. Another ingenious idea for avoiding the supposed excess of acid, was to separate the black atraiuentous precipitate, wash it, and again diffuse it with water thickened with gum. This, indeed, makes a very good ink, but with the capital defect of not remaining so long suspended in the liquor, and especially of not fixing itself to the paper like common ink, but rather only slightly adhering like a weak gum varnish, and was readily washed off by water. Hence it appears that the acid of the salt of iron acts as a kind of mordant or intermede, between the atrementous precipitate and the paper, and causes a degree of chemical union between them; a real advantage which this species of ink possesses over all the lamp-black, or China inks, which, indeed, are rather black varnishes.
With regard to the gummy ingredient, the effect of which is rather mechanical, it was found that any other gum-mucilage would answer as well; but not glue, isinglass, nor animal jelly of any kind. Besides, as these latter putrify by keeping, this alone would be a strong objection.
Sugar is sometimes added to ink. Tt makes it flow somewhat easier from the pen, and gives it when dry a gloss which is admired by some. It has this quality, however, of making it very slow in drying, which in most cases is an inconvenience.
On account of the great improvements to the black atramentous dye produced by adding sulphate of copper, some have recommended this addition to common ink ■which is composed of the same materials; but it does not appear that the same advantage is here obtained, and Dr. Lewis thinks it an useless addition.
From the above observations, Dr. Lewis gives the following receipt for the composition of ink: put into a stone or glass bottle, or any other vessel, three ounces of finely
powdered galls, one onnce of green vitriol, one ounce of logwood finely rasped' or bruised, one ounce of gum-arabic, and a quart of soft water: shake the bottle well, and let the ingredients stand in a moderately warm place for a week or ten days, shaking it frequently in the day. It is then fit for use; but a little before it is put into the ink-stand, it is better to shake the bottle that the colour may be more uniformly diffused.
To prevent the ink from moulding, Hoffman recommends half a doren cloves to be bruised with the gum arabic, and put into the bottle. This appears a useful addition. Instead of water alone, where a very tine ink is wanted, white wine, or vinegar and water, may be used.
If the ink be wanted for use in a very short time, the galls and logwood may be boiled for half an hour in the water, adding a little more to supply the waste, and the decoction while hot strained off through a cloth, and the gum arabic and cloves, and the sulphate of iron, both in fine powder, added to the decoction when in the bottle and shaken. The ink will then be fit for use almost immediately after the Utter ingredients are dissolved. It will be improved by adding to the bottle some pieces of gall-nut coarsely bruised. Ink kept in a close bottle is always rather pale; but it blackens by exposure to air in a few hours; and probably in this way the colour is somewhat more durable than if it were brought by previous exposure to its full colour at once.
It has been mentioned that sugar renders ink slow in drying. Advantage is ingeniously taken of this property in enabling it to give one, and sometimes two impressions on soft paper, when strongly pressed. In this simple way letters are copied in merchant's counting-houses, and offices of business. A little sugar is mixed with the ink, the writing-sheet is laid on the copying press, a blank sheet of porous and damped paper is put over it, alid by the pressure of the machine a perfect facsimile of the writing is struck off, sufficiently legible for all purposes.
This ingenious method saves a vast quantity of labour usually bestowed in copying letters, and besides prevents all possibility of mistakes.
Sometimes the ink of very old writings is so much faded by time as to be illegible. Dr. Blagden, (Philosophical Transactions, vol. Ixxvii.) in his experiments on this subQq z
ject, found that in most of these the colour might be restored, or rather a new body of colour given, by penciling them over with a solution of prussiate of potash, and then with a dilute acid, either sulphuric or muriatic; or else vice versa, first with the arid, and then with the prussiate. The acid dissolves the oxide of iron of the faded ink, and the prussiate precipitates it again of a blue.which restores the legibility of the writing. If this be done neatly, and blotting paper laid over the letters as fast as they become visible, their form will be retained very distinctly. Pencilling over the letters with an infusion of galls also restores the blackness to a certain degree, but not so speedily nor so completely.
The blackness of common ink is almost instantly and irrevocably destroyed by the oxymuriatic acid, and hence any writing may be effaced by this method completely. To prevent this mischief, which might often be a serious one, several additions have been proposed to common ink, of which by far the best 'is lamp-black or charcoal, in impalpable powder, on which the acid has no effect. The lamp-black should be of the least oily kind, as it does not readily mix with the ink, and some pains must be taken to incorporate them. On this account perhaps common charcoal is preferable. About a quarter of the weight of the vitriol used will be amply sufficient. This will not fade by age.
Ink, China or Indian. The well known and much admired Indian or China ink, is brought over in small oblong cakes, which readily become diffused in water by rubbing, and the blackness remains suspended in it for a considerable time, owing to the extreme subtlety of division of the substance that gives the colour, and the intimacy with which it is united to the mucilaginous matter that keeps it suspended.
Indian ink does, however, deposit the whole of its colour by standing, when it is diffused in a considerable quantity of water. Dr.Le wis, on examining this substance, found that the ink consisted of a black sediment, totally insoluble in water, which appeared to be of the nature of the finest lamp-black, and of another substance soluble in water, and which putrified by keeping, and when evaporated left a tenacious jelly exactly tike glue or isinglass. It appears probable, therefore, that it consists of nothing more than these two ingredients, and probably may be imitated with perfect accuracy by using a very fine jelly, like isinglass or size,
and the finest lamp-black, and iucorpomtm? them thoroughly. The finest lamp-black. known is made from ivory-shavings, and thence called ivory-black.
Ink, printer's. This is a very singular composition, partaking much of the nature of an oil varnish, but differing from it in lie quality of adhering firmly to moistened paper, and in being to a considerable degree soluble in soap-water.
It is, when used by the printers, of the consistence of rather thin jelly, so that it may be smeared over the types readily and thinly, when applied by leather cushions, and it dries very speedily en the paper without running through to the other side, or passing the limits of the letter.
The method of making printer's ink is thus described by Dr. Lewis. Ten or twelve gallons of nut-oil are set over the fire in a large iron pot, and brought to boil. It is then stirred with an iron ladle, and whilst boiling, the inflammable vaponr rising from it either takes fire of itself or a kindled, and suffered to burn in this way for about half an hour, the pot being partially covered so as to regulate the body of the flame, and consequently the heat communicated to the oil. It is frequently stirred during this time, that the whole may be heated equally, otherwise a part would be charred and the rest left imperfect. The flame is then extinguished by entirely covering the pot The oil by this process has much of its unctuous quality destroyed, and when cold is of the consistence of soft turpentine, and is then called varnish. After this it is made into ink by mixture with the requisite quantity of lamp-black, of which about two ounces and a half are sufficient for sixteen ounces of the prepared oil The oil loses by the boiling about au eighth of its weight, and emits very offensive fumes. Several other additions are made to the oil during the boiling, such as crusts of bread, onions, and sometimes turpentine. These are kept secret by the preparers. The intention of them is more effectually to destroy part of the unctuous quality of the oil, to give it more body, to enable it to adhere better to the wetted paper, and to spread on the types neatly and uniformly.
Besides these additions, others are made by the printers, of which the most important is generally understood to be a little fine indigo in powder, to improve the beauty of the colour.
Red printer's ink, is made by adding to the varnish, about half its weight of venni
lion. A little carmine alto improves the colour. (Encycl. Arts & Metiers, vol. iii. J). .MB.)
Inks, coloured. Few of these are used except red ink. The preparation of theseX is very simple, consisting either of decoctions of the different colouring or dying materials in water, and thickened with gum-arabic, or of coloured metallic oxides or insoluble powders, merely diffused in gum-water. The proportion of gum-arabic to be used may be the same as for black writing ink. All that applies to the fixed or fugitive nature of the several articles used in dying, may be applied in general to the use of the same substances as inks.
Ink, red, is usually made by boiling about two ounces of Brazil wood in a pint of water, for a quarter of an hour, and adding to the decoction the requisite quantity of gum, an I about half as much alum. The alum both heightens the colour and makes it less fugitive. Probably a little madder would make it more durable.
Ink, blue, may be made by diffusing Prussian blue or indigo through strong gumwater.
Ink, yellow, may be made by a solution of gamboge in gum-water.
Most of the common water-colour cakes diffused in water, will make sufficiently good coloured inks for most purposes.
Inks of other colours may be made from a strong decoction of the ingredients used in dying, mixed with a little alum and gum arabic. For example, a strong decoction ot Brazil wood, with as much alum as it can dissolve, and a little gum, forms a good red ink. These processes consist in forming a lake, and retarding its precipitation by the gum. See Lake.
On many occasions it is of importance to employ an ink indestructible by any process, that will not equally destroy the material on which it is applied. Mr. Close has recommended for this purpose 2.S grains of copal in powder dissolved in 2UO grains of oil of lavender, by the assistance of gentle heat, and then mixed with 2J grains of lamp black and hah'a grain of indigo: or 120 grains of oil of lavender, 17 grains of copal, and tin grains of vermilion. A little oil of lavender, or of turpentine, may be added, if the ink be found too thick. Mr. Sheldrake suggests, that a mixture of genuine asphaltum dissolved in oil of turpentine, amber varnish, and lamp black, would be still superior. When writing with common ink has been
effaced by means of oxygenized muriatic acid, the vapour of sulphuret of ammonia, or immersion in water impregnated with this sulphuret, will render it again legible. Or if the paper that contained the writing be put into a weak solution of prussiate of potash, and when it is thoroughly wet a sulphuric acid be added to the liquor, so as to render it slightly acidulous, the same purpose will be answered.
Mr. Haussman has given some compositions for marking pieces of cotton or linen, previous to their being bleached, which are capable of resisting every operation in the processes both of bleaching and dying, and consequently might be employed in marking linen for domestic purposes. One of those consists of asplialtum dissolved in about four parts of oil of turpentine, and with this is to be mixed lamp black, or black lead in fine powder, so as to make an ink of a proper consistence for printing with types. Another, the blackish sulphate left after expelling oxygen gas from oxide of manganese with a moderate heat being dissolved and filtered, the dark grey pasty oxide left on the filter is to be mixed with a very little solution of gum tragacanth, and the clutli maiked with this is to be dipped in a solution of potash or soda, mild or caustic, in about ten parts of water.
Among the amusing experiments of the" art of chemistry, G exhibition of sympathetic inks holds a distinguished place. With these the writing is invisible, until some reagent gives it opacity. We shall here mention a few out of the great number, that a slight acquaintance with chemistry may suggest to the student. 1. If a • weak infusion of galls be used, the writing will be invisible till the paper be moistened with a weak solution of sulphate of iron. It then becomes black, because these ingredients form ink. 2. If paper be soaked in a weak infusion of galls,and dried, a pen dipped in the solution of sulphate of iron will write black on that paper, but colourless on any other paper. 3. The diluted solutions of gold, silver, or mercury, remain colourless upon the paper, till exposed to the sun's light, which gives a dark colour to the oxides, and renders them visible. 4. Most of the acids or saline solutions being diluted and used to write with, become visible by heating before the fire, which concentrates them, and assists their action on the paper. 5. Diluted prussiate of potash affords blue letters when wetted with the solution of sulphate of iron. 6. The solution of cobalt