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 ma terials; 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 ounce of green vitriol, one ounce of log wood finely rasped or bruised, one ounce of gum-arabic, and a quart of soft water ; shake the bottle well, and let the ingre dients stand in a moderately warm place for a week or ten days, shaking it fre quently 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 dif fused.
To prevent the ink from moulding, Hoffman recommends half a dozen 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 'fine 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 oft' 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 latter ingredients are dissolved. It will be improved by adding to the bot tle some pieces of gall-nut coarsely bruis ed. 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 pre vious exposure to its full colour at once.
It has been mentioned that sugar ren ders ink slow in drying. Advantage is ingeniously taken of this property in ena bling 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, and 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 eisually 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 illegi ble. Dr. Blagden (Philosophical Trans
actions, vol. lxxvii. ) in his experiments on this subject, found that in most of these the colour might be restored, or rather a new body of colour given, by pencilling 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 acid, 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 re stores the legibility of the writing. If this be done neatly, and blotting paper laid over the letters as fast as they become vi sible, 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, se veral 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, per haps, common charcoal is preferable. About a quarter of the weight of the vi triol 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 wa ter. Dr. Lewis, on e3. nining this sub stance, 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 petrified by keeping, and when evaporat ed left a tenacious jelly exactly like glue or isinglass. It appears probable, there fore, 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 in corporating them thoroughly. The finest lamp-black known is made from ivory shavings, and thence called ivory-black.