Wherever it is possible, the same becks, pane, &c., should be reserved for the same class of colour.
The selection of the water used in dyeing is also of great import- -01B._ once. As a rule, the nearer it approaches to distilled water, the better. For many delicate aniline and grain colours, condensed steam-water, free from grease, should be employed. The woollen yarn dyers of Berlin, and the calico-printers of Alsace, are indebted to the character of the water at their command for no small part of their success. To this rule, there are two exceptions: madder and its derivatives require the presence in the dye-water of a certain quantity of lime, which is easily supplied by adding ground chalk, or acetate of lime ; blacks and other sad colours may also be more economically dyed with hard waters, such as those from deep artesian wells.
The heat required in dyeing may be produced either by open fires beneath the pans, or by steam, applied either in a steam-jacket, in the form of coils of steam-pipe, or by blowing steam direct into the liquid.
Calico-Printing.—This art differs from dyeing, both in its object and its means. The purpose of the printer being to produce upon pieces regular designs in two or more colours, he is compelled to limit the action of his materials to particular portions of the surface to be thus ornamented. Hence his colours are not liquids, but pastes, or pulps; and they are applied to those parts of the cloth, where they are to take effect, by a stamping process, performed either by hand or by machinery. These conditions involve no small difficulty ; the dyer can and does "work to shade," adding, as circumstances may require, a little more of his ingredients, or prolonging the action. But the printer has no opportunity of modifying his materials after they are once brought into contact with the fibre.
The foremost peculiarity of the printer's colours, mordants, or mixtures of both, as distinguished from those of the dyer, is that they require to be thickened. For this purpose, a great variety of materials are used :—flour, starch, whether of grain or of the potato ; natural gums, such as arabic, senegal, and trsgacanth ; and artificial gums, such as dextrine, which, in its various modifications, is known as British gum, calcined starch, leiocome, gomeline, &c. There are also mineral bodies
occasionally employed for this purpose, such as China-clay, and siliceous earth. These various sub stances are not all equally fitted for all purposes. No small part of the art of the printer lies in the skilful selection of a right thickener. The properties of the chemicals present, the actions to which the mixture has to be exposed, the character of the design, and the manner of printing, whether by hand or by machine, have to be duly taken into account. For machine work, much smoother and finer thickeners are required than for block work, even the presence of grit in the gum or starch being a serious inconvenience. Sometimes one of the ingredients in a colour—an acid or an acid salt—is not added till the mixture has become cold, lest at a high temperature it might convert a portion of the starch into glucose, and thus greatly modify the expected reaction. The thickening power of these bodies differs greatly, 10-12 oz. gum tragacanth per gal. being as effective as 20 oz. starch, 22 oz. flour, or 8-9 lb. calcined farina. The larger the quantity of thickening employed, the lighter, generally speaking, will be the resulting colour. As a rule, the more the colours, by judi cious thickening, can be kept upon the face of the cloth, and prevented from sinking in, the brighter will be the colour, the clearer the design, and the more economical the working.
In the earlier days of the art, printing was exclusively performed by hand, with wooden blocks, upon which the designs were produced in relief, by cutting away portions of the wood, and letting in slips of sheet copper. This method of printing is still found exceedingly useful for the production of particular effects, though for general work it is quite superseded by the swifter and more econo mical cylinder-machine.