The art of producing upon calico or cotton cloths patterns or designs combining a variety of colours, so as to produce an agreeable and pleasing effect. This ingenious business, as at present conducted, may be considered as one branch of the art of dyeing; and as it depends chiefly upon the proper application of a few compounds, called mordants, we shall commence our description of the process by explaining briefly the nature of colours, and the uses of mordants. The colouring substances employed in this art may be divided into two classes, viz. substantive and adjective. A substantive colour is one which of itself is capable of producing a permanent dye; such are woad and indigo, and the solutions of some metals, particularly those of iron, cobalt, gold, platinum, and silver, which give various colours, according to the processes by which they are prepared. By adjective colours are meant all those which are incapable of imparting permanent colours without the aid of certain intermedia, which having a greater affinity both for the colouring matter and for the cloth, than the colouring matter has for the cloth, forms, as it were, a bond of union between the two latter substances.

These intermedia are called mordants: the principal ones at present in use in this country are the acetate of iron, the acetate of alumina, and the various solutions of tin. In the usual process of dyeing with adjective colours, the entire piece of cloth is steeped in the mordant, and some time afterwards is submitted to a bath of the particular kind of colouring matter which is to be imparted to it; but in printed goods, certain parts require to be left white, a pattern, therefore, of those parts which are to be coloured is cut in relief on blocks of wood, or plates of metal, and the mordant being applied over the whole surface of the pattern, the pattern is then impressed upon the cloth, and when the cloth is subsequently passed through the colouring bath, only those parts to which the mordant has been applied will receive a permanent stain; for although the whole piece will be coloured, those parts which are untouched by the mordant will be easily restored to their original whiteness by washing and exposure to the air. Previous to printing, the cloth undergoes a variety of processes, termed the preparation. The first of these is termed dressing, and consists in passing the cloth very rapidly over a cylinder of iron, at nearly a white heat, or over a broad flame of gas.

It is next steeped for twenty-four hours in a weak alkaline lye, at the temperature of about 100°, and is afterwards boiled in a solution of potash, which is called ashing, and is then well washed, to free it entirely of the alkali. The next process is called souring, which consists in immersing the cloth in water containing about one-twenty fifth part of its weight of sulphuric acid, and being again well washed and dried, the preparation is completed. Previous to the ordinary description of printing, the goods are calendered, which consists in passing them through a set of rollers, which gives them a gloss; but for what is termed copper-plate printing, or cylinder work, the calendering is omitted. In printing fast colours, the printer proceeds as follows: he lays the calico, which has been already smoothed by calendering, upon a strong thick table, covered with a woollen cloth, and proceeds to apply one or more mordants, as the case may require, for fixing the intended colours. The mordants are applied by means of wooden blocks, to the surface of which the pattern, cut out of thick plates of brass or copper, is firmly fixed.

When the mordant is ready, it is either mixed with flour paste, or a thick aqueous solution of gum Arabic, gum Senegal, gum tragacanth, or of what is called British gum, which is merely common starch calcined and pulverized. In this state the mordant is spread upon a piece of fine woollen cloth, strained tight upon a broad hoop. This is called the sieve, and is placed within another hoop, called the case, covered with sheep skin, or oil cloth, and the sieve within its case is placed in a tub of gum water, and is ready for use. The mordant is applied to the surface of the sieve by means of a brush, which is called teezing; and should the mordant be colourless, as, for instance, the acetate of alumina, some fugitive dye is mixed with it, to make the pattern obvious to the workman, who, taking the block containing the pattern in one hand, applies it gently to the surface of the sieve, so that a sufficient quantity of the thickened mordant may adhere to the figures. He then applies the block thus charged to the calico, giving it a blow with a small mallet, and continues applying the block alternately to the sieve and to the calico, until he has gone over the whole piece.

When the piece is intended to contain a variety of colour, several different mordants are thus applied, as the different colours require different mordants to fix them and render them permanent. The calico is now removed to a room heated by flues, in order to be dried; but this is much better effected by an apparatus shown in the annexed engraving, and consisting of a series of cylinders a a made of copper or tinned iron, and filled with steam, and round which the calico is made to pass in succession. Beneath every two cylinders is a vane b b moved by a steam engine, which agitates the air, so as very much to facilitate the drying; indeed, so rapidly are the goods dried by this mode, that although the fabrics be wound from the heap c on to the first cylinder perfectly wet, they become thoroughly dry by the time they have passed over the whole apparatus, and fall in a perfect state on the heap d. After drying, the pieces are passed by means of a winch through water at various temperatures, with a little cow-dung mixed with it, in order to remove that portion of the mordant which is not actually combined with the cloth, and which might otherwise stain the white or unprinted parts.