Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/764

690 dyeing, the pieces are passed through weak sulphuric acid, not only to remove the oxide of copper, which has been precipitated, but also to fix the indigo on the calico, by liberating it entirely from its lime combination. Various other resist pastes are employed when it is desired to print other colours over the white portions, as for example, when orange or yellow grounds are desired the mixture consists of a salt of copper to resist the blue indigo vat, with a salt of lead to produce the chromate of lead by treatment with bichromate of potash after the blue dyeing is complete. The late J. Lightfoot of Accrington devised and patented, in 1867, a method of printing reduced indigo simultaneously with the mordants for madder, garancin, and other dye colours, by which a combination of indigo blue with other tints can be obtained of perfect clearness and brilliancy, without resorting to the complex and tedious processes involved in discharging colours, repeated printings, (fee., when colours are blocked on a blue ground. The success of his process depends on the preparation of a pulp of indigotin and tin, in which he carefully avoided any excess of tin salt, so that it does not attract the alizarin in the madder beck, and in consequence leaves the indigo effects clear and unclouded.

China Blue.—This style of print is obtained by printing on the calico a mixture composed of pulverized indigo and sulphate of protoxide of iron, to which is sometimes added orpiment, and thickened with British gum. The pieces so printed are passed alternately, by means of rollers, first into a milk of lime, and then into a solution of sulphate of protoxide of iron, when there ensues one of the most in teresting phenomena of calico-printing ; for as fast as the blue indigo is reduced into white indigo, instead of being dissolved by the lime of the bath, it is retained with force through the molecular attraction of the fibre of the calico, and prevented leaving the cloth until it is fixed by the exposure of the piece to the oxygen of the atmosphere. The pieces then only require to be passed into weak sulphuric acid, washed, and dried, in order to be com pleted. This process is not now much used.

Pencil Blue is obtained by reducing blue into white indigo, by boiling it for several hours with protochloride of tin and alkali. When the indigo is well reduced, citrate of soda and starch are added ; and after the whole is carried to the boiling-point, the calico is printed with it, passed into a milk of lime, washed, and dried.

Aniline Slack is a most beautiful and fast colour, pre pared by mixing a salt of aniline with a metallic salt and an oxidizing agent, which substances on exposure gradually react on each other, and develop a rich velvety black. There is thus produced one of the most unalterable colours known, resisting soap, acids, and even chlorine to a remark able extent. It is a colour of recent introduction, having been first printed by Mr John Lightfoot of Accrington, in 1859, and patented in 1863 ; but it is now in very exten sive use, many different methods for producing it having been devised and patented. The most extensively employed system is that patented in 1871 by Mr Lightfoot, the originator of the colour, which is thus given by Mr Dreyfus 30 pints chlorate of ammonia, prepared either by means of tartaric acid and chlorate of potash, or by another process without tartaric acid, are thickened with 6 to 8 Ib wheat starch and 6 to 8 Ib best dark British gum. When this colour has been well boiled, it is allowed to get cool, and then 7 pints of a solution of the purest and most neutral aniline salt that it is possible to get are added ; this solution is made with 8 ft of salt to the gallon of water, with three-quarters to one pint of sulphide of copper paste. After the mixture is printed, the pieces are lightly dried and hung in the ageing room in a moist warm atmosuhere, with the dry bulb thermometer about 80 and the wet bulb 10 lower. From thirty hours to tvo days are required to develop the colour, the printer judging of the progress of the ageing by the tint. According to Mr William Mather an ordinary ageing machine will effectually &quot;age&quot; the aniline black, if only a proper current of air is maintained of the requisite moisture and tempera ture. This is readily accomplished by having a properly contrived outlet to the chamber at the top, the draught of which is controllable, and inlets for fresh air in the sides of the chamber. This mode Mr Mather states is in successful operation, and by simple mechanical contrivances may be universally adopted. When the pattern has assumed a deep bottle-green tint, the goods are removed and passed through a solution either of bichromate of potash, of car bonate of soda, or of both mixed, and then soaped and dried. When aniline blacks are to be further printed with steam colours or dye colours, as is commonly the case, the treat ment of the pieces after ageing is modified according to the necessities of the case.

Chrome Black is an oxidation colour produced by printing with logwood liquor and passing the goods through a bath of bichromate of potash, when the colouring principle of the logwood hasmatoxylin- undergoes a special oxidation. The colours obtained from catechu arc also fixed by oxidation, the colouring principle catechuin being only soluble in its unoxidized condition, and when oxidized after printing, it yields various browns and drabs, which have a very high degree of fastness.

The various processes of printing included under this head are of modern introduction, but they have steadily risen in importance, till now they embrace the largest part of the art, having so largely and rapidly superseded all other styles that the process would appear to be destined to become the predominant style of the future. Indeed, to such perfection have steam colours been brought that in some Continental establishments, it appears, the dye- house has been altogether closed and steam colours only now printed. As compared with the printing of dye colours the &quot; topical &quot; or steam colour style is simple, direct, and expeditious, requiring no tedious dyeing, and only light soaping, clearing, and finishing operations. By the dyeing processes alone the range of shades which it is practicable to print on one piece is strictly limited by what the mordants and their various combinations will yield with the particular dye-stuff used. But in steam colours there- is no limit to the number and variety of shades which may be produced, each colour-box on the cylinder printing- machine containing the whole ingredients essential to the production and fixation of a separate and distinct shade or colour. In addition to this the steaming process can be and is extensively employed to supplement the effect of madder-printed or Turkey red goods by printing steam colours into the whites, produced either by resist pastes or by discharges printed on the dyed texture. The distinguishing peculiarities of steam colours consist 1st, in printing direct and at one operation on the cloth the whole of the materials of the dye and its fixing agent properly mixed and thickened; and 2d, in submitting the printed cloth to the influence of steam, which effects the fixation of the colour. The effect produced by the com bined heat and moisture of the steaming process is, in the case of certain combinations, purely mechanical, while in others a chemical reaction ensues. In the printing of what are termed pigment colours, or, in other words, insoluble coloured powders such as used by painters, they are simply mechanically fastened or glued to the cloth by means of albumen, or some body of similar constitution, which coagulates and becomes insoluble on the application of a