Styles of Printing

Indigosol 0 is printed in admixture with gum tragacanth thick ening and sodium nitrate, being afterwards developed by passing through a bath containing hot formic or oxalic acid; in some in stances hot acetic acid may be used. Thus ion parts indigosol 0, 35o parts hot water and 55o parts tragacanth thickening and 30 parts sodium nitrate is printed on to cotton fabric, which is then dried in hot air. Blue is developed by treating for a few seconds at about 8o° C in a bath containing 4 parts formic acid (9o%), 8 parts common salt and i oo parts water. The Soledon products and other indigosols may be applied in a somewhat similar way. As these materials can be used in conjunction or juxtaposition with colouring matters of totally different groups (both as regards dyeing and chemical constitution), such as insoluble azo colours and aniline black, they are especially useful. Rowe and Bean (1927) have given valuable information with regard to the devel opment of the indigosols and allied products with different oxidizing agents.

Other Vat Colours.

Indanthrene, duranthrene, caledon and cibanone colours as well as those of the algol and alizarine indigo series may be applied by methods analogous to those described for indigo. Some very fast effects may be obtained, but difficulty is experienced by printers, owing to the fact that if the backgreys become stained with the colours, it is almost impossible to bleach them. This is a serious matter if customers' cloth is used for backgrey. Some of these colours require much alkali for their fixation and this is liable to attack the blanket. A steaming method for the printing of these colours which gives satisfactory results is the following :-600 parts alkaline thickening (a mixture of British gum and gum senegal), ioo colouring matter, 8o stan nous oxide 5o% paste, and 5o glycerine. Hydrosulphite formalde hyde may be used in place of stannous oxide as the reducing agent. Duranthrene yellow and cibanone blue 3G are colours suitable for printing in this way. After the goods have been steamed and the colour fully developed it is best to wash out the alkali from the cloth as thoroughly as possible. Sulphur colours and sulphurized vat colours are best printed with hydrosulphite formaldehyde. Aniline Black.—Various methods for the oxidation of aniline, but particularly the prussiate method described under DYEING, may be utilized in printing. All are difficult to print well. Some difficulty is experienced in steaming or ageing, and special ageing appliances, with suction elements to carry away acid vapours and to maintain a relatively pure atmosphere of steam, have been patented. From the same source patents, in which the

amount of acid used in the formation of the black is reduced to a minimum, figure conspicuously. The following is an ungreenable black which requires no afterchroming : 7.5 parts starch, 30o gum tragacanth mucilage, 32 aniline, 44 aniline salt, 4.5 paraphenylene diamine dihydrochloride, 4o formic acid (90%) 34 boracic acid, 41 chlorate of soda, 40 copper sulphide (24%). Print this mixture on to the cloth, age, wash and soap. The ageing process is carried out in an apparatus fitted with suction elements between the layers of cloth.

Basic Colours are of importance where brightness is the most important consideration. The usual method is to add the dyestuff to the prepared thickening, then some acetic, citric or tartaric acid, and then a mixture of tannic acid and acetic acid; e.g., 20 parts methylene blue, 5o acetic acid (40%) 120 water and 72o starch paste are heated together, 10 ground tartaric acid cooled, and 8o tannic acetic solution (50%) are added. After printing the cloth is steamed.

Insoluble Azo Colours may be employed in a variety of ways, the most important being : (a) Printing a pattern in thickened naph thol and afterwards passing through a diazo solution. (b) Printing a diazo solution on cloth prepared in various naphthols. In these processes procedure is much the same as in DYEING (q.v.), except that in (a) the naphthol is thickened with British gum and in (b) the diazo solution is thickened with gum tragacanth. Various naphthols may be used and a large variety of shades obtained by utilizing naphthol A.S. and allied products. A good black can be obtained with A.S., S.W. and fast black base L.B. The colours possess great fastness and are but little affected by hot ironing (a defect of the beta naphthol colours). The latter such as para red and alpha naphthylamine maroon are used for cheap work. (c) The rapid fast colours (stabilized diazo compounds or nitrosamines mixed with analido compounds of beta oxynaphthoic acid) can be applied directly in printing. They are rather expensive but find considerable application because they are readily developed by treating the cloth after printing with hot dilute acetic acid. It is necessary to add a little potassium chromate to the printing colour if these are printed in combination with basic or chrome colours. They are conveniently used in combination with indi gosols or Soledon colours. Everest has shown (1928) that the naphthols may be applied to silk from a soap bath and in the absence of caustic alkali. The method is patented for silk printing.