When these materials are well incorporated, they are poured on a plate of cast iron, made warm, and oiled, in order that the composition may be easily detached from it.

Ledges of wood are put on the plate to keep the thickness of the composition uniform, which when congealed, but still warm, is cut into sticks, like Indian ink.

14. Indian Ink. - The genuine article, which is used by the Chinese for writing with a brush, as well as for painting upon their soft, flexible paper, is ascertained by experiment and information to consist of lamp-black and size, animal glue, with the addition of perfumes or of other substances not essential to its quality as an ink. The fine soot from the flame of a lamp or candle, received by holding a plate over it, mixed with clean size from shreds of parchment of sheep and goat skins, will make an ink equal to that imported. We have been in the habit of using, during many years, both the genuine and the imitation Indian ink indifferently, without being able to discover that either merits a preference.

15. Lithographic Drawing Ink. - This composition is the same as the ink used for writing upon stone and lithographic transfer paper, already described; the artist rubbing it down usually upon a slab, as Indian ink, for his use.

16. Letter-press Printing Ink is a very smooth and jet black oil paint. The consistence and tenacity of the oil in this composition are greatly increased, and its greasiness diminished, by means of fire. Linseed oil, or nut oil, is made choice of for this use. The nut oil is supposed to be the best, and is accordingly preferred for the black ink, though the darker colour it acquires from the fire renders it less fit for the red. It is said, that the other expressed oils cannot be sufficiently freed from their unctuous quality. Ten or twelve gallons are set over the fire in an iron pot, capable of holding at least half as much more; for the oil swells up greatly, and its boiling over into the fire would be very dangerous. When it boils, it is kept stirring with an iron ladle; and if it do not of itself take fire, it is kindled with a piece of flaming paper or wood. It is found that mere boiling, without setting it on fire, does not give it a sufficiency of the drying quality. The oil is suffered to burn for half an hour or more, and is then extinguished by covering the vessel close, and excluding the air.

The boiling is continued with a gentle heat, till the oil has attained the proper consistency, in which state it is called varnish.

It is necessary to have two kinds of this varnish, a thicker and a thinner, (from the greater or less boiling it has received,) which are occasionally mixed together, to suit different purposes; for that which answers well in hot weather, becomes too thick in cold, and large characters or type do not require such stiff ink as the small. The thickest varnish, when cold, may be drawn into threads, like glue; and the workmen taking out small quantities, from time to time, judge of the proper degree of boiling required, by testing its tenacity in that manner. The oil loses by the boiling about one-eighth of its weight. The varnish readily mingles with fresh oil, and it will unite with mucilages, into a mass that is afterwards diffusible in water. About one-seventh part, by weight, of lamp-black is added to the varnish, to give it the depth of colour. Boiled with caustic alkali, a soapy compound is formed, and printers availing themselves of this fact, are in the habit of cleaning their types by soap-makers' lees and a brush.

It is said that when very new oil is used in making ink, it does not readily dry without the addition of litharge, or the oil of turpentine, and these additions (which are not necessary in old oil) cause it to stick very hard to, and clog up the types.

17. Red and other coloured Printing Inks, are made from linseed oil, boiled into a varnish, as described in the black ink, with the addition of some dry pigment of the required colour, which is ground up with the varnish, with a stone and muller in the manner of oil paint. Thus, for preparing the bright red printing ink, vermilion is ground up with the varnish, in such quantity as will give the required depth of tint. In like manner for blues, yellows, oranges, greens, etc. the Prussian blue, indigo, orpiment, chrome, red and orange lead, verdigris, and in general the pigments used by house painters, are similarly combined with the varnish.

18. Copperplate Printing Ink is of a somewhat similar kind to that used for type printing, but the oil is less boiled, and the varnish is in consequence much more fluid; and instead of lamp-black, they either use the black imported from Frankfort, (which is said to be the charcoal of vine twigs, prepared in a peculiar manner,) or when this cannot be procured, or is too costly, the finest ivory black they can obtain.

19. Lithographic Printing Ink differs from that used in typography, only in being a much thicker varnish; and the lamp-black which is used as the colouring matter is not mixed with it in the mass, but small portions of the varnish are taken from time to time, as it is required, and the lamp-black then only ground up with it for immediate or very early use. See Lithography.

20. Removing Stains of Ink. The stains of ink on cloth, paper, or wood, may be removed by almost all acids; but those acids are to be preferred which are least likely to injure the texture of the stained substance. The muriatic acid, diluted with five or six times its weight of water, may be applied to the spot, and after a minute or two may be washed off, repeating the application as often as may be found necessary. But the vegetable acids are attended with less risk, and are equally effectual. A solution of the oxalic, citric (acid of lemons), or tartaric acids in water, may be applied to the most delicate fabrics, without any danger of injuring them; and the same solutions will discharge writing, but not printing ink. Hence they may be employed in cleaning books that have been defaced by writing on the margin, without impairing the text. Lemon-juice, and the juice of sorrel, will also remove ink stains, but not so easily as the concrete acid of lemons, or citric acid.