The mode of working is influenced by the character of the goods, and the following notes will be found useful by the union dyer.
Very little difficulty will be met with in dyeing such light fabrics as Italians, cashmeres, serges and similar thin textiles lightly woven from cotton warp and woollen weft. When deep shades (blacks, dark blues, browns and greens) are being dyed it is not advisable to make up the dye-bath with the whole of the dyes at once. It is much better to add these in quantities of about one-fourth at a time at intervals during the dyeing of the piece. It is found that the affinity of the wool for the dyes at the boil is so much greater than is that of the cotton that it would, if the whole of the dye were used, take up too much of the colour and then would come up too deep in shade. Never give a strong boil with such fabrics, but keep the bath just under the boil which results in the wool dyeing much more nearly like to cotton.
On Union Flannels.--In this class of goods it is important that the soft open feel of the goods be retained as much as possible, and for this purpose no class of dyes offers so many advantages as the direct colours. Only one bath being required, there is not the same amount of manipulation needed in the dyeing operation, hence there is less risk that the soft feel and woolly structure will be affected. As no mordants are needed there is nothing to impart a harsh feel to the fabrics.
On Dress Goods, Suitings and Coatings.--A large quantity of fabrics for gentlemen's suits, coats and cloths in general are now made from wool and cotton. Formerly the dyeing of these offered many difficulties before the application of the direct dyes was properly understood. Now, however the ease with which such dyes may be applied has given considerable impetus to this class of goods, and the trade has grown by leaps and bounds during recent years, and has been one cause of the great cheapening of clothes which has occurred in the same period. The dyeing of the goods with the direct colours offers very little difficulty, and only requires that a little attention be paid, particularly to goods in which the cotton either appears on the surface forming a design, or is spun or twisted together with the wool.
A good deal of shoddy is used in making the cheaper class of these goods, and it is quite natural that such "artificial wool" behaves differently from pure wool, not only with regard to its shade resulting from mixing and working together differently dyed waste wools, but also on account of its possessing a greater affinity for all kinds of dye-stuff than raw wool; this in consequence of the carbonisation and washing processes it has undergone, and also of the mordants which the material may retain from previous processes. Therefore (and especially in dyeing light shades on goods manufactured of shoddy) only a small quantity of soda or borax is to be added to the dye-bath and severe boiling is to be avoided. Wherever it is possible goods which are to be dyed in light shades should be made from the palest materials, and the dark qualities only used for goods which are to be dyed in dark shades.
This rule can, of course, not always be adhered to. Quite often a light and bright shade is to be dyed on comparatively dark material. This cannot be achieved by simply dyeing it, the goods must be stripped or bleached before dyeing. For this purpose either energetically reacting, oxidising reducing agents are applied. Of the former, bichromate of potassium is principally used. Boil the goods for half to three-quarters of an hour with 3 to 5 per cent. bichromate of potassium, 2 to 4 per cent. oxalic acid, and 3 to 5 per cent. sulphuric acid, wash in a fresh warm bath charged with soda in order to entirely neutralise the acid which has remained in the goods, or else the wool would be dyed too deep a shade. In some cases hydrosulphite has proved a useful reducing agent; it can be easily prepared from ordinary bisulphite of soda in the following manner. Add 10 oz. ammonia (0·9 specific gravity) to a gallon of bisulphite of soda, 32° Tw.; then add slowly under a brisk stirring 10 oz. zinc-dust, and let the entire mixture settle well, using only the clear solution. Treat the goods from fifteen to twenty minutes in a bath of 140° F., to which first add at the boil 3/4 oz. acetic acid, 10° Tw., per gallon water, and then 4 to 6 gallons clear hydrosulphite solution per 100 gallons liquor. Then rinse very well and dye in the usual manner; avoiding, however, too high a temperature. As on this class of goods dark shades are mostly dyed, the goods need only very rarely be stripped.
Bright Yellow.--Use 2 lb. Thioflavine S in a bath which contains 4 lb. Glauber's salt per 10 gallons of dye-liquor.
Good Yellow.--A very fine deep shade is dyed with 2-1/2 lb. Diamine Gold, and 24 lb. Diamine Fast Yellow A in the same way as the last. Here advantage is taken of the fact that while the Diamine Gold dyes the wool better than the cotton the Diamine Yellow dyes the cotton the deepest shade, and between the two a uniform shade of yellow is got.
Pale Gold Yellow.--Use a dye-liquor containing 4 lb. Glauber's salt in every 10 gallons, 2-1/2 lb. Diamine Fast Yellow A, 2 oz. Indian Yellow G, and 3-1/2 oz. Indian Yellow R. In this recipe we use in the two last dyes purely wool yellows, which dye the wool the same tint as the Fast Yellow A dyes the cotton.
Bright Yellow.--Use in the same way as the last 2-1/2 lb Diamine Fast Yellow B and 3 oz. Indian Yellow G.