Styles of Printing

Application of Pigment

the introduction of coal-tar colours, pigments and lakes played a more important part in textile printing and they are still largely used for certain styles of work. They form a series of colours more difficult to work than those already mentioned, but very fast to soap and light. Pigment colours, being insoluble mineral precipitates or lakes, can only be fixed on the fibre mechanically; consequently they require to be applied in conjunction with vehicles which cause them to adhere to the fabric in much the same way that paint adheres to wood. Of these vehicles, albumen is the most important and the best. It forms a smooth viscous solution with cold water, mixes readily with all the colours used in pigment printing, and possesses the property of coagulating when heated to the temperature of boiling water. When cloth printed with colours containing albumen is passed through hot steam or hot acid solutions, as in the indigo discharge style, the albumen coagu lates, forming a tough insoluble colloidal deposit, which firmly fixes on the fibre any colour with which it is mixed.

The colours chiefly employed in pigment printing are : chrome yellow and orange, Guignet's green or chrome green, artificial ultramarine, lamp black for greys, the various ochres for golds and browns, zinc oxide, vermilion and its substitutes, and occasion ally lakes of the natural and artificial colouring matters.

Dyed

Style.—Before the introduction of the azoic colours of the naphthol A.S. series, practically the only reliable method of obtaining fast shades in printing was by printing mordants on to cotton and then dyeing in natural colours such as madder, persian berries, logwood and other dyewoods. Alizarine has entirely super seded madder but logwood and persian berries are sometimes used. Other alizarine and chrome colours may be dealt with in this way. The application of the mordant in printing involves (I) the pre liminary preparation of the cloth with oil, (2) printing on the mordant usually in the form of acetate, (3) ageing, (4) fixing (dunging is said to be more efficient than substituted fixing agents because it removes thickening material as well as excess of mor dant) and (5) dyeing (see DYEING) in alizarine. In order to obtain perfect white in the unprinted portions, cloth after washing and soaping is passed through a very dilute solution of bleaching liquor. The process has been mainly used for obtaining red, pink, lilac and black prints, by depositing varying strengths of alumina and iron and dyeing in alizarine and logwood.

The thickened mordants used in the madder style are called colours, not because they contain any colouring matter, but be cause they give definite shades when dyed in alizarine. For madder

red the following method applies:-6T Red. too parts wheat starch, 5o parts flour, goo parts red liquor 6° Tw. (from which the red acquires its designation), 20 parts olive oil and 0.5 parts magenta (to sight the mordant). The goods are then passed at full width through a fly dunging machine containing Soo gal. water, 15 parts chalk, 21 parts phosphate of soda and 70-85 parts cow dung.

A second dunging is carried out in a vessel similar to a dye beck and the goods are worked for 20-3o min. at 50-6o° C. Malt or bran added to the dunging liquor accelerate the removal of starch but this is more necessary when using one of the substitutes for dung, i.e., phosphate of soda (i1-6 parts by weight), binar senate of soda (2-5 parts), or silicate of soda 32° Tw. (2o parts), with 7.5 parts of chalk per 1,000 parts water. After fixing, the goods are washed and dyed in 5% alizarine (20% paste) with the addition of Turkey red oil 5% and 0.5% chalk. Soaping and clear ing completes the process.

The following table gives the ingredients necessary for obtaining six colours by printing the mordants on one piece and afterwards dyeing in a single bath with 4.5% alizarine (20% paste) and acetate of lime, proceeding as before. Aniline black may be printed along with red and black liquors. It is usual to employ only one or two colours, in this style of printing, with perhaps two concen trations of red or black liquor for light and dark shades of red and purple.

effects and white. With two rollers the following four colours can be obtained on a light indigo blue : blue ; green, by overprinting indanthrene yellow; white, by discharging parts of the blue; and yellow, by applying the discharge on parts coloured green. Azo colours resist the action of bichromate and can be used in this style of printing by incorporating mixtures for their production with the chromate printing discharge for blue.

As compared with oxidation discharges (chromate and chlorate) the Leucotrope hydrosulphite discharge possesses a great ad vantage in that the darkest shades of indigo can be discharged to a pure white without any danger of tendering the cloth. Hydro sulphite is the reducing agent for the indigo, but the leucotrope forms either a means of removing indigo white from the fibre (Leucotrope W. forms an alkali soluble yellow compound with in digo white) or a means of producing coloured discharges (Leuco trope 0. forms a yellow compound which is not removed by washing in alkali). Strong Discharge White: 160 parts zinc oxide (50% paste), ioo parts Leucotrope W., 24o parts hydrosulphite formaldehyde, 40 parts anthraquinone (3o% and paste), 46o parts British gum thickening.