The term "ink " is used to denominate a great variety of fluid or semi-fluid compounds employed in the permanent delineation of objects upon paper, stone, glass, metals, leather, textiles, and other grounds. The chief desiderata in most inks are a capacity of flowing readily from the writing instrument, while possessing sufficient body to prevent spreading and blotching, combined with depth and permanency of colour. The latter naturally depends in a great measure upon the physical and chemical characters of the article written upon, and especially upon the presence or absence of bleaching agents. The composition of inks varies as widely as do the purposes to which they are applied, hence they may be classified as follows: - Black writing-ink, coloured writing - ink, copying - ink, engraving-ink, indelible inks, Indian ink, invisible ink, marking-ink, miscellaneous inks, printing-ink, stamping-inks.
The following are among the most approved recipes: -
(a) 1 lb. bruised galls, 1 gal. boiling water, 5 1/3 oz. sulphate of iron (copperas) in solution, 3 oz. gum-arabic previously dissolved, and a few drops of an antiseptic, such as carbolic acid. Macerate the galls for 24 hours, strain the infusion, and add the other ingredients. (6) 12 oz. bruised galls macerated for a week in 1 gal. cold water, 6 oz. sulphate of iron in solution, 6 oz. mucilage of gum-arabic, and a few drops of antiseptic, (c) 12 lb. bruised galls, boiled for ah hour in 6 gal. soft water, adding water to replace that evaporated; strain, and reboil the galls in 4 gal. more water for 1/2 hour; strain, and boil with 2 1/2 gal. more water; strain, and mix the liquors. Add 4 1/2 lb. coarsely powdered sulphate of iron, and 4 lb. gum-arabic in small pieces; agitate till the ingredients are dissolved, and filter through a hair sieve. This will make about 12 gal. of good ink. (d) 2 lb. bruised galls, digested in 2 qt. alcohol at a temperature of 104° to 140° F. (40° to 60° C); when about half the alcohol has evaporated, add 3 qt. water; stir well, and strain through a linen cloth. To clarify the solution, add 8 oz. glycerine, 8 oz. gum-arabic, and 1 lb. sulphate of iron dissolved in water.
Stir thoroughly from time to time for a few days, allow to settle, and put up in well-stoppered bottles for preservation. The addition of too much sulphate of iron is to be avoided, as causing the ink soon to turn yellow. Ink thus prepared is said to resist the action of light and air for at least 12 months, without suffering any change of colour, (e) Digest in an open vessel 42 oz. coarsely-powdered galls, 15 oz. gum-senegal, 18 oz. sulphate of iron, 3 dr. aqua ammonia, 24 oz. alcohol, and 18 qt. distilled or rain water. Continue the digestion till the fluid has assumed a deep black colour. (f) To good gall-ink add a strong solution of fine Prussian blue in distilled water; the ink writes greenish blue, but afterwards turns black; it is said that it cannot be erased either by acids or alkalies without the destruction of the paper, (g) Take blue Aleppo galls free from insect perforations, 5 1/2 oz.; bruised cloves, 1 dr.; cold soft water, 3 1/2 pints; purified sulphate of iron, 1 1/2oz.; sulphuric acid by measure, 35 minims; sulphate of indigo, in the form of a thin paste, and which should be neutral or nearly so, 1/4 oz. Digest together in a closed vessel, with occasional agitation, for two weeks, the galls, cloves, and water.
Then filter through a piece of cotton cloth, and press out as much of the liquid as possible from the sediment. Dissolve in this completely the powdered sulphate of iron, stir in briskly the acid, then the indigo, and filter the liquid through the paper (filter-paper). In all the inks described in this section, nut-galls are introduced for the sake of their tannip acid. For this purpose they are not equalled by any other tannin-yielding substance; and a Commission lately appointed by the Prussian Government to decide what was the best ink to be employed for official purposes, selected that made from galls as being the foremost of all for durability. For cheaper inks the galls may be replaced by catechu, sumach, and a host of other astringent substances. The antiseptic (carbolic acid, etc.) is added to prevent the formation of mould.
(a) A decoction of logwood is first made by boiling 10 lb. logwood in enough water to produce 80 lb. of the decoction. To 1000 parts of this logwood extract, when cold, is added 1 part of yellow (neutral) chromate of potash (K2Cr04), stirring rapidly. It is ready for use at once, without any addition; but it possesses the great fault of soon becoming thick.
This may be corrected by (6) adding corrosive sublimate or any other antiseptic, (c) Boil 10 oz. logwood in 20 oz. water; then boil again in 20 oz. more water, and mix the two decoctions; add 2 oz. chrome alum, and boil again for 1/4 hour; and 1 oz. gum-arabic. The product is 25 oz. deep black ink. (d) Runge, in 1848, discovered that a dilute solution of the colouring matter of logwood, to which had been added a small quantity of neutral chromate of potassium, produces a deep black liquid, which remains clear, does not deposit, and may be employed as an ink. Perfectly neutral litmus paper is not affected by it, it does not attack pens, it is very cheap, and so easily penetrates writing-paper that it cannot be removed by washing even with a sponge - in a word, it has all the properties of an excellent ink. On exposure to the air in an inkstand, it sometimes decomposes very rapidly, its colouring matter being deposited in the form of large black flakes, which leave a colourless liquid above them. This gelatinisation is a great defect in this ink, particularly as one does not know the precise conditions that determine it.
Different means have been proposed to prevent this action; the best seems to be that of the addition of carbonate of sodium, recommended by Bottger. To prepare this ink, take extract of logwood, 15 parts; water, 1000 parts; crystallised carbonate of sodium, 4 parts; neutral chromate of potassium, 1 part. Dissolve the extract of logwood in 900 parts of water, allow it to deposit, decant, heat to ebullition, and add the carbonate of soda; lastly, add drop by drop, with constant stirring, a solution of the neutral chromate in 100 parts of water. The ink thus obtained has a fine bluish-black colour; it flows well from the pen, and dries readily. The chrome ink powder of Platzer and the acid ink of Poncelot are imitations of the original ink of Runge. (e) 10 lb. best logwood is repeatedly boiled in 10 gal. water, straining each time. The liquid is evaporated down till it weighs 100 lb., and is then allowed to boil in a pan of stoneware or enamel. To the boiling liquid, nitrate of oxide of chrome is added in small quantities until the bronze-coloured precipitate formed at first is redissolved with a deep blue coloration. This solution is then evaporated in a water bath down to a syrup, with which is mixed well-kneaded clay in the proportion of 1 part of clay to 3 1/2 of extract.