The wet goods should be immersed in the cold or lukewarm bath, and turned constantly for a few minutes only, before taking them out, wringing them, and hanging them up to oxidize. As soon as the color sets, which is shown generally, by the change of shade and which never takes more than, say, twenty minutes if the materials are well opened up, the goods should be brightened in a hot bath of good, neutral, olive oil soap, and then finished as previously described. It will be remembered that several, indeed most of the best Vat colors do not develop their final shade at all, until after the soaping process. When carefully done, this process will give exceedingly fast and quite brilliant colors, without injury to the strength of the goods. _Comparative Results of Vat Dyes and Sulphur Dyes on Silk._—It is hard to get full shades with Sulphur colors because it is generally necessary to heat the dye-bath, and this, owing to the powerful alkaline properties of the sodium sulphide, is very injurious to the silk. Besides this, the sulphur dyes are much less brilliant than the Vat dyes, and have no good red or orange shades in the whole class. They accordingly should not be used, excepting where no other are available, or, as will be described in a later chapter, when doing “resist stencilling” on silk. On the other hand, such very unusual advantages do some of these new Vat dyes possess, for the dyeing of silk for special purposes, that large quantities of Helindones, Thio Indigoes, and other good specimens of this class are being sold, at comparatively very high prices, to manufacturers of fine shirtings where the patterns are made by weaving fine lines or figures of brightly dyed silk into the linen or cotton fabric. Until the introduction of these dyes in the last two or three years these shades could not have been produced fast enough for this purpose. Sulphur dyes can also be used on silk without injuring the goods, by taking the precautions described earlier in this chapter. The shades, however, are quiet and dull, as compared to those produced by other classes of dyestuffs; and it is almost, if not quite, impossible to get a good full red and, especially, a good scarlet, by using these colors. Silk properly dyed with Sulphur colors is extremely fast to washing. But these dyes, unlike the best Vat colors, are as a rule quite sensitive to bleaching agents, and therefore are not so well adapted for general use on “embroidery fast” silk. CHAPTER XIII IMITATION AND ARTIFICIAL SILK Owing to the high price of pure silk and the bad wearing qualities of the highly adulterated silks, described in the last chapter, there has been for a long time a strong demand for a fabric which would combine as far as possible the strength and wearing power of the one, with the cheap price of the other, while still retaining the lustre and “scroop” and characteristic appearance of both.