Yellow Discharge: 46o parts British gum thickening, and 200 parts hydrosulphite formaldehyde, dissolve, cool and add i oo parts Leucotrope 0., 4o parts anthraquinone (30% paste) and 200 parts Discharge Printing.—This depends upon the action of acids, alkalis, oxidizing and reducing agents for the destruction of dyed colours. It stands to reason that colours which are very fast require drastic oxidizing or reducing agents for their decomposi tion, but the former are difficult to apply without danger to the printed fabric. Sometimes two reagents play a part in the proc ess. One is printed on the dyed fabric and reacts with the sec ond, through a solution of which the printed fabric is passed. An advantage of this method is that fine delicate patterns can be discharged on a dark ground with a crispness of definition which is difficult to attain with a blotch roller.
Iron and alumina mordants are discharged by printing with citric acid, so that a white pattern on a coloured ground is ob tained on dyeing. Basic colours are destroyed with alkalis. The chrome discharge is produced by printing the goods with a solu tion of sodium or potassium bichromate thickened with British gum, passing through a mixture of oxalic acid and sulphuric acid. White and coloured discharges on indigoid colours are obtained in this way.
Yellow: 32 lb. chrome yellow pigment, 3 gal. 5o% albumen solu tion, 1 gal. thick tragacanth mucilage, and -I gal. oil (vegetable), 12 lb. bichromate of soda neutralized with 4 gal. caustic soda, 70° Tw., and 1 gal. water.
Print, dry, pass through a "beck" (i.e., a bath) containing: ioo gal. water, 5o lb. sulphuric acid (168° Tw.), and so lb. oxalic acid, then wash well and dry.
A green discharge is obtained with Guinet's green, a red with vermilion and brown with burnt sienna in place of chrome yellow. These colours resist the action of the bichromate and the acid treatment which follows printing coagulates the albumen. Another method (Freyberger) consists in printing on a thickened solution of sodium nitrate and, after drying, running through sulphuric acid of so° Tw.
With colours of the indanthrene series, indigo gives compound shades and, as these are not destroyed by bichromate, over print ing this with a roller of another pattern produces three colour zinc oxide (50% paste). Glucose may be used as the reducing agent for discharging indigoid colours. This is especially useful in producing coloured discharges with insoluble azo colours. Leuco
trope cannot be used with indanthrene colours as it acts as an efficient resist to their fixation.
A very ancient method of ornamenting fabric is what is known as the batik style (see BATIK and TEXTILES). Imitations of this style are obtained by printing wax from engraved roller plates and stencils. Different colouring is obtained by putting on another pattern or part of a pattern in wax and redyeing. When the mad der style is used for the colouring, the wax printed goods are mordanted and then dyed, the wax resist is broken, the cloth is dipped in the indigo vat, and a red, white, blue and chocolate effect is obtained, the latter by the superposition of blue on red. By tinting the cloth in chrysamine (direct cotton colour) a buff instead of white is obtained.
In machine printing resin is used in place of wax: for this pur pose rollers heated with an internal electric heater have been patented by F. Ashton and the Calico Printers' Association. Resin-printed cloth fixes chromium from hydrosulphite formalde hyde mixtures instead of resisting it. Bichromate of soda and formosul are the best for this purpose. If resin-printed cloth is dyed in indigo before mordanting, the batik cracks appear in light blue on a dark ground, the shade of the ground being slightly modified by the superposed mordant colour. Other white resists are obtained by printing metallic salts, flowers of sulphur and lactic acid, or ammonium nitrate under the ordinary printing re sists. The composition of the best resist for indigo printed by the glucose process is as follows : i 5o parts flowers of sulphur, 5o parts lactic acid 50%, and Boo parts 30% gum Senegal solution.
Sulphur is liable to etch the roller immediately following the resist roller, and this may be avoided by the use of chemical re sists (Reserve Salts W and 0, Kalle and Co.), which however do not give good results if crushed by the next roller, so can only be used with advantage for single colour resists. Indigosols can be used with success in resist printing. Leucotrope (15o parts Leuco trope 0. 85o British gum thickening) will prevent the fixation of any vat dye printed over it.