Ink

Ink. The term "ink" may be applied to any liquid which can be employed for writing upon paper or other fabric, leaving after drying a more or less permanent and indelible record. Such liquids have been used for many centuries, but accurate information regarding the composition of ancient inks is but scanty, so that little is definitely known. They were probably, however, similar to our present Indian ink. It is convenient to divide inks into those employed for writing and those used for printing. Of the former black is the colour chiefly used, and the ordinary black writing-ink is composed essentially of a compound of iron and gallic acid, which is held in suspension in a thin gum solution. It is prepared by thoroughly macerating nutgalls with hot water and then adding to the decoction a solution of copperas, together with the quantity of gum necessary to give the liquid the required consistency. As proportions the following may be taken: - Nutgalls, 12 lb.; copperas, 5 lb.; Senegal gum, 5 lb.; water to 12 gallons. In many inks logwood or indigo is also added, the latter being used in most of the blue-black inks, which, though blue at first, quickly dry to a deep black colour. Other materials have been employed and different inks produced not containing the above materials, but have enjoyed little popularity. For red ink a decoction of Brazil mood, to which a small quantity of chloride of tin has been added, is usually employed. Solutions of cochineal or of carmine may also be used, but the writing with these compounds is not of as permanent a nature as with the former substance. Blue ink is best made by dissolving Prussian blue in a solution of oxalic acid, the pigment being first purified by treatment with a mineral acid - e.g. hydrochloric acid. Inks of other colours may also be prepared by the use 0:.' suitable dyes, the so-called aniline colours being well adapted for the purpose. Copying-inks, by means of which copies of the writing may be taken on a damp sheet of paper pressed upon it, are prepared from ordinary writing-inks by the addition. of sugar, gum, or other such substance. Marliingink, used for production on linen of writing which can withstand washing, is usually prepared by the solution of the nitrate or tartrate of silver in ammonia, together with a little gum to give consistency. A colouring material is also usually added, but the indelible writing is entirely due to the decomposition of the silver salt. Numerous chemicals are also employed for the formation of sympathetic inks, in which the characters only become visible after the application of some process.

to the writing. Thus a solution of sugar of lead (lead acetate) yields writing which becomes visible if treated with sulphuretted hydrogen. By use of solutions of cobalt salts, drawings, etc., may be obtained in which the markings, etc., become green on warming, but again invisible on cooling; and these compounds are used in production of the so-called chameleon pictures. A solution of nutgalls, if used as ink, becomes visible if treated with a solution of copperas, and many other means may be adopted for similar purposes. Printing-inks, not being used in the same manner as writing-inks, require totally different properties. Thus, while they do not require to flow as easily, they should dry more rapidly, and not be affected, or to but a small extent, by water, etc. What is found best adapted for printing purposes is a thick, drying oil into which is thoroughly mixed lampblack, or, if coloured inks are desired, any other permanent pigment. The oil usually employed is linseed oil.

It is first boiled and allowed partially to burn; sliced soap and a quantity of powdered resin are added and well stirred, after which the still warm liquid is poured over the lampblack, to which a little indigo may be added, and thoroughly stirred and mixed before being allowed to cool. For coloured printing-inks the manufacture is essentially similar, but other pigments, as vermilion, Prussian blue, yellow ochre, etc., are employed. Lithographic inks are also prepared from lampblack mixed up with shellac, soap, wax, tallow, and gum solutions; while most of the so-called indelible inks consist of the same pigment suspended in a suitable medium. [Indian Ink.]