Calico Printing

Calico Printing is the art of applying chemicals and colours to the surfaces of textile fabrics in such a way that patterns of a permanent character are produced. As practised in Europe, the industry requires the exercise of the highest degree of chemical knowledge and mechanical skill, and it differs very widely from the primitive methods which have been adopted in the East for centuries, and which are there still in operation. In Persia and in India the manufacture of chintz for the European market was carried on largely until 1721, when a law was passed in this country to protect home weavers by prohibiting the wear of all printed calicoes whatsoever. This measure followed the imposition of a very heavy duty in 1700. Calico, or cotton cloth, took its name from Calicut, in Malabar, and here the art was in full activity. Its principal secrets, as the mummy coverings prove, were, however, known to the Egyptians in the days of the Pharaohs. In India, carved hand blocks, one for each tint, are to this day employed by the handicraftsman to imprint the patterns, but the chief merit of Indian tissue stuffs has always been in the brilliancy of their natural dyes and not in the fineness of the printing. India has lost its great export trade of cotton manufactures, the competition of Manchester haying been too severe, and Lancashire and Glasgow remain the centres of calico-printing in England, in both districts the art being first introduced in the early part of the last century. In Manchester it was established in 1763-5, but nearly a hundred years earlier (1676), when cotton printing had been imported from India to Holland, and thence to other parts of Europe, a Frenchman set up the first print works close to London.

Grey calico, or cotton cloth, has in this country to be prepared for ornamentation by singeing and bleaching. In block-printing the pattern is engraved upon sycamore wood, and by means of a "toby" it is possible, with one block, to imprint several colours at a single operation. The bulk of calico-printing in this country is done by machines. For the wooden blocks, engraved copper rollers or cylinders, 3 feet 6 inches long and 6 inches in diameter, are substituted. As each separate colour or shade in the pattern calls for its own cylinder, the stock of them which has to be kept by the manufacturers entails an immense expenditure. One machine may carry as many as twenty cylinders, but the number generally is about eight. These cylinders, together producing the design, do not print, except in some processes, in the sense that paper is printed with ink by stereotype. Their purpose generally is to convey to the cotton cloth, exactly where it is required, a chemical agent called a mordant, which, if it were not for the admixture of a little "sightening" colour, would almost be invisible. The mordant is an agent for fixing the dye which will hereafter be applied to the fabric. Red liquor (acetate of alumina) is one mordant, and black liquor (oxides of iron) another, and there may be a mixture of the two. Copper, lead, and tin furnish other mordants. Usually each mordant is printed on the cloth before the addition of the dye, but sometimes they are put on together. The mordants require to be thickened with white flour, potato starch, and other substances by which they are rendered soluble and converted into a dextrin similar to gum arabic in its properties. This preparation is to facilitate printing. Varying depths of shade are obtained by regulating the quantity of the mordant, and with one dye solution, and with different mordants, or mordants of different strengths, the full pattern of, say, ten colours, so far as the printing goes, may be completed at one operation in the machine, each colour or shade having its own cylinder and mordant box.

A calico-printing machine consists of a large cushioned central drum, or bowl, and against this the engraved copper cylinders are pressed, an endless blanket passing between the bowl and all the cylinders. Each cylinder is maintained in position by means of radiating mandrils, which also support a colour-box, in which revolves a wood cloth-covered roller, which takes up the mordant and distributes it upon the surface of the engraved copper cylinder, with which it is constantly in contact. The calico, in tension, guided by the blanket, and travelling with a "back cloth," receives the impression of all the cylinders in turn, as it passes between them and the central drum. Attached to each cylinder are two sharp blades of steel, one called the colour "doctor," its work being to shave off the excess of colour, or mordant, which is left on the engraved parts only; and the other, termed the "lint doctor," which keeps the cylinder free of all impurities which may come from the cotton cloth. Obviously the cylinders have to be adjusted most perfectly to secure a satisfactory result in placing the colours in their proper position.

The foregoing process of mordant printing is adopted in the "madder style," and the design then appears upon the cloth in feeble greys, giving little promise of its future richness of colour. In order to fix the mordant thoroughly in the fibre, the cotton pieces, after leaving the printing machine, are dried by being passed over revolving cylinders in a closed chamber into which a current of heated air is injected. They are "aged" in a confined but large chamber filled with moist and warm air, whereby in about twenty minutes, by means of a system of rollers between which the cloth is "threaded," is accomplished the work which in the old days took four days' hanging in the air to perform. In the "ageing" the acetic acid in the mordant is in great part disengaged in fumes, whilst a sub-salt is fixed in the fibre. The calico is now slowly passed through a weak bath of alkaline silicate or arseniate of soda, mixed with a little chlorate of potash, at a given temperature, with the object of completing the decomposition of the mordants and of separating those portions which are not thoroughly combined with the cotton, so as to prevent all danger of their blotting unmordanted parts. The materials used to thicken the mordants are also dissolved and removed. Cow dung, exclusively, was used formerly instead of the chemicals, and hence this process is still called "dunging." The mordanted pieces are now ready for the dye "beck "or cistern, and the winch apparatus used imparts a circulating movement to the pieces, which are prevented from becoming entangled, and are made to take the dye equally during the hour and a half or two hours they remain passing in and out of the liquor. The dye-liquor is heated by steam. After they are removed from the beck the pieces are well washed and boiled in order to "clear" the colours. Before this is done the mordanted parts which have taken up the colour are dull-looking, whilst the portions which should be white are pinkish. Soaping removes the excess of colour, and brightens the tints. The pieces are made continually to revolve in becks in one temperature, and are washed out, squeezed, and rewashed. It will now be seen how madder, or its derivatives, is affected differently by different mordants. Madder was at one time the most important of all dye-stuffs known to calico printers. It was used by the Egyptians in combination with alumina and iron mordants. In brilliancy and variety of shade and colour it stood unequalled, one dyeing operation sufficing to produce pinks, reds, purples, violets, puce, and black, all permanent under the action of light and of soap. Alizarine is its chief colouring principle, and since 1869, when a method of artificially preparing it from anthracene was discovered, it has been substituted largely for the dye from the madder root. In the printing from alizarine, and from garancin, another preparation of madder, the process is the same. The colours given by alizarine are, however, not so "fast" as those yielded by madder. Fast is a term applied to those colours which resist the action of light, air, water, alkali, dilute acids, and soap solution. With the same solution of alizarine the alumina mordant gives red, the iron mordant purple, and a combination of the two chocolate.

As the opposite of the madder style there is the "padding" style, in which the whole of the surface of the cloth is mordanted, the pieces passing through a trough and between rollers. They are then dried and the design is sometimes obtained by "discharging" the colour wherever required by printing with citric acid or salt of potash, which has the effect, when the material has gone through all the intermediate stages and has reached the dye-beck, of preventing the colouring matter from adhering to the parts protected by the acid, and which thereupon show up white on a coloured ground. The white parts may receive other colours afterwards.

Indigo, which is a very valuable dye, requires to be treated in a particular manner owing to its being insoluble in water. It can, however, be made soluble if put in water with green copperas and slaked lime, a process of deoxidation which changes the blue indigo into soluble white indigo. White indigo takes up oxygen with great facility, and thus regains its blue. The plan, therefore, is to dip the calico hooked on to a wooden frame into vats holding the soluble or white indigo, and then expose it to the air in order to recover the temporarily lost colour. The pieces are dipped again and again for darker shades; and they are passed through "sours," or a solution of sulphuric acid, permanently to fix the indigo. Amongst other oxidation colours are, besides indigo, catechu, aniline black, and some of the logwood blacks, which do not require a mordant but need to be developed and fixed by exposure to the air or by some oxidising agent. When a white device, or "figure," on a blue ground is desired the pattern is printed with a "resist" paste, which is removed after dyeing; the resist being frequently made of sulphate of zinc or nitrate of copper and soap, thickened with gum. It prevents the indigo or other colour from attaching itself to the parts it covers, and which may, if not left white, be treated with other colours subsequently.

Topical colours are those which are printed upon the top of the cloth, and are fixed by the action of steam. These insoluble pigments, such as vermilion, cadmium, chrome yellow, ochre, umber, and the non-poisonous and less expensive painters' colours, in the form of a fine powder, are mixed with albumen and then printed. The steam to which the pieces are afterwards exposed coagulates the albumen and fixes the pigments mechanically. Ordinary steam colours are those which are fixed by chemical agency. When steam colours are used the work in many stages is much lighter than that attaching to the madder style. Aniline colours form a very important branch of the steam department. In the steam style the colour-boxes on the printing machine contain not mordants merely but all the materials necessary to the production and fixing of a distinct colour or shade, so that one advantage is the direct printing at one operation, without a dyeing process to follow, and another advantage is the fixing of the colours in a great variety by the agency of steam alone. Before the printed calico is ready for the market a number of finishing processes are necessary, in order to impart a glossy and better appearance to the article.