In order that ink may be more durable in the manuscript, the paper may be advantageously dipped in a solution of galls ; this obviates the fading on the back of the paper ; i. e. in the part to which the ink has sunk deepest, where that change is most apt to commence. Dr. Lewis found this to be very effectual in his experiments. Others have recommended that the paper should be dipped in prussiate of potassa, which makes any tendency to change of colour to consist in the acquisition of a deep and rich blue tint.
But as this species of ink, after the best preparation, is apt to decay, Dr. Lewis made attempts to form one of still more durable materials. He found that a composition of black carbonaceous matter, such as lamp black, with var nish, and half the weight of a thick mucilage of gum arable, formed an ink which, though it was easily rubbed out with water on common paper, proved in every respect durable when applied with a pen to bibulous paper. The manu scripts of the ancients were w ritten with lamp black and gum ; and the Chinese use a similar composition fur all their writings, the s um: which is sent to Europe under the name of China ink, which they apply with a stiff hair pen cil, fixed in the end of a reed. \V hen vinegar is used in stead of water in tempering it, the ink sinks deepar into the paper. Dr. Lewis ingeniously suggested, as an improve ment, the union of the ancient with the modern method, by adding a small portion of the ancient composition, or of Indian ink, to our common ink. In this case, cotton must be used in the ink-stand, to prevent the settling of the black powder.
These methods are sufficient to secure every advantage, where the effacing of manuscripts is not done by design. liut it has become, in recent times, an object, on many' oc casions, to guard against frauds of obliteration. These are more easily executed since the discovery of the oxymuria tie acid, and its power in effacing all inks made of the gal lie acid, or vegetable astringents, with iron. For prevent ing the possibility of this, when it is dreaded, an admixture of lamp black or other burnt carbonaceous matter is ef fectual, and ought to be in larger proportion than on other occasions. Finely ground indigo is recommended by sonic along with the lamp black. Others employ finely i levigated manganese, and others a solution of indigo in centrated sulphuric acid. The editor of the ?nnales des
vol. ii. p. '06, observes, that the common ink maybe rendered incapable of being discharged by any action which the paper can withstand, if, instead of water, the expressed juice of green vegetables be used, such as the lathyrus, the sambuelis niger, or common grass.
Indian or China ink, being an article possessed of valuable properties, experiments were made by Dr. Lewis to ana lyze and to imitate it. He found that the adhesive ingredient in it was an animal glue, and he formed very good imitations of it by means of glue and lampblack. The superior delicacy ofihe imported article seems to depend on the black. It brings different prices, according to its fineness; and this depends on the kinds of oil from which it is produced. Various oils are turned in that country, in chambers made for the purpose. Du Ilalde gives three receipts for this composition, on Chi nese authority. In one of them, the conglutinating ingre dient is gum tragacanth ; this must have formed an ink dif ferent from that brought to us from China. In another it is thin size, and in a third the size is mixed with a decoc t ion of certain vegetables, which probably impart no quali ty excepting smell.
Indelible ink, for marking linen, without being liable to obliteration by washing, is merely a solution of nitrate of sil ver, with which the letters are traced after the part to be written on has been dipped in a solution of soda, and dried with a strong heat.
Inks of various colours may in general be made by using a strong decoction of the ingredients used for dying, mixed with a little alum and gum arable.
Red ink from an infusion of logwood.
Green ink from a solution or acetate of copper, with gum arabic and white sugar.
Blue ink from indigo, ground with white of eggs, and brought to the due consistence by water.
Yellow ink from an infusion of crocus, with alum and gum arabic.
Sympathetic ink is a substance with which writings may be formed, which are invisible till they are subjected to ,Gine process, which immediately renders the whole dis tinct. This purpose was collided among the ancients by means of milk, or sonic other viscous substance, which was tendered legible by means of soot thrown overthe writ ing ; part of it adhering wherever the lines were drawn, while from every other part it was blown entirely off.