Another drawback is that indigo-dyed goods, especially of the heavy full shades, are apt to “rub.” This can best be avoided by always using a well-reduced bath; by washing with boiling soap after each dip; and by building up the deep shades by successive dippings in moderately weak vats, rather than by obtaining the shade, once for all, by using a very strong, concentrated dye-liquor. For many hundreds, and even thousands, of years, indigo has been universally recognized as the most permanent and most valuable blue dyestuff for cotton and indeed for woolen goods. For the latter purpose it is now but little used, thanks to the introduction of the exceedingly fast dyestuffs of the Acid and Mordant classes. But for cotton it is still considerably used, for fast shades. THE MODERN VAT COLORS Up to a very recent date indigo was the only dyestuff, of any importance at any rate, that was used in the manner just described, and produced colors fast to light and to washing. During the past three or four years, however, the attention of the dyeing chemists has been directed to this question, and at least five of the great dye houses have introduced dyestuffs covering a great range of colors which, when dyed in the same way as indigo, not only rival but distinctly surpass that color in permanence as well as beauty. =Names.=—These dyestuffs, while known generally as the Vat colors, have been given special class names by their manufacturers, as follows: Algol (_Elberfeld_); Ciba (_Klipstein_); Helindone (_Metz_); Indanthrene (_Badische_), and Thio Indigo (_Kalle_). The Cassella Company are just introducing the first members of their series, to be known as Hydrons. =List of Selected Dyestuffs=:— Badische— Indanthrene Claret, B, Extra Indanthrene Yellow, G Indanthrene Blue, G C D *Indigo pure Cassella— *Hydrone Blue, R *Hydrone Blue, G Elberfeld— Algol Red, 5 G Algol Yellow, 3 G Algol Blue, 3 G Kalle— *Thio Indigo Red, B G *Thio Indigo Scarlet, S Thio Indigo Brown, G *Indigo, K G Klipstein— Ciba Red, G Cibanone Yellow, R Ciba Green, G Ciba Blue, 2 B Ciba Violet, R Metz— Helindone Red, 3 B Helindone Fast Scarlet, R *Helindone Yellow, 3 G N *Indigo M L B, 6 B N.B.—The dyestuffs marked * will dye in a lukewarm or even cold bath.