For dyeing by the Vat method the dye-pot is two-thirds filled with warm water, at about 120° F. (when the finger can hardly bear the heat), and one or two tablespoonfuls of caustic soda are added—enough to make the bath decidedly alkaline. The dyestuff, preferably first mixed up with some hot water, to thin the paste, is stirred into the liquid, and then to this is added sodium hydrosulphite, in powder, or preferably dissolved in water, until the color of the bath changes from blue, first to green, and then to greenish yellow, with a bluish-green coppery scum. If the bath is bright yellow, too much hydrosulphite has been used, and some more indigo should be added; or, if this is not desirable for fear of getting too dark shades, the bath should be exposed to the air and stirred frequently until the color is right. If the bath, on scraping aside the scum, looks blue, or even markedly green, it needs a little more hydrosulphite. If, after reduction, the bath looks yellow but turbid, it probably needs more alkali. Into this bath the material is placed, and stirred around until thoroughly saturated—the temperature being kept about 120° F. for heavy goods, to assist penetration. Light goods can be dyed equally well in a lukewarm, or even a cold bath. The goods are then taken out, wrung lightly by hand, and are carefully passed two or three times through the wringer, to get the color evenly distributed. They are then shaken out and hung up in the air to oxidize. In fifteen or twenty minutes, after the color has changed, they should be rinsed well in two or three waters, to get rid of all traces of the caustic alkali, and then boiled for several minutes in a soap bath, to wash off the loose dyestuff and prevent rubbing. This after-treatment with boiling soapsuds is of even more importance in the case of the other Vat dyes than it is with indigo, for with most of them the oxidation is not completed in the air—and so the color is developed as well as brightened by the soap bath. It is very important, when working with these Vat colors, to remember that hot solutions of caustic alkali are very hard on the hands and that, therefore, rubber gloves are extremely useful, if not essential. Stains left on hands, clothes, and utensils, although difficult to remove by washing, are almost instantly dissolved by warm solutions of hydrosulphite with a little soda or other alkali in them.