_Results._—Colors produced by synthetic indigo are clear and clean, but not brilliant. If the slightly purplish shades of natural indigo are desired, they can be obtained with special brands—Indigo R, or Indigo RR, _Metz_—or by mixing small quantities of Algol Red B, _Elberfeld_, or Thio Indigo Red B, _Kalle_, with the indigo before reducing it. It is generally supposed that the characteristic shade, the so-called “bloom” of natural indigo, was due to the presence of small quantities of a reddish dyestuff, known as indigo red. As a matter of fact, however, the method of dyeing has more to do with this than the composition of the dyestuff. For instance, if the indigo is very thoroughly reduced in the vat before the goods are immersed, as is generally the case in the modern hydrosulphite method, and the bath is made up with fresh reducing agent for each dyeing, the resultant color will be a very clear, rather greyish, shade of blue without any purple lustre. If, however, the dyestuff is not very perfectly reduced, as was generally the case with the old fermentation vats, and the bath, from standing in the air, has a heavy scum on the top, and is greenish rather than clear yellow in color below the surface, then the dyed fabrics will be apt to show the marked purplish tone which is so characteristic of the older indigo dyeings. _Uses._—While of less importance than it used to be before the discoveries of the last few years, the use of indigo for dyeing cotton, especially for the craftsman, is not to be neglected. It furnishes, easily and rapidly, in one bath, without either boiling, mordanting, or after-treatment, exceedingly pleasant, soft shades which are fast to both light and washing. For resist dyeing, such as Tied and Dyed work, Resist Stencil work, and Batik, it will be found particularly useful, because the fabric can be dyed in the cold. Indigo possesses, however, certain disadvantages, especially for the professional dyer, which it shares with the other Vat dyes described below, and which prevent it, and the other Vat dyes, from being used as widely as the Salt colors or even the Sulphur colors. In the first place these dyes are all of them expensive. They cost more than most others, pound for pound of the dry color, and full shades need much larger proportions of them in the bath. Then it is difficult to dye to shade with them, because the color, as a rule, alters so much when exposed to the air. In practice, when dyeing large quantities of goods to the same shade, it is customary to divide the materials into several lots of the same weight; and to make a strong “stock solution” of the dyestuff, properly reduced with alkali and hydrosulphite. By making up a fresh vat for each lot of goods, using exactly the same volume of water and of “stock solution,” and working each lot for the same length of time and at the same temperature, even results can be produced with much less trouble than by dyeing to shade by the eye.