_Acid Dyes, to be used on Silk._—Any of the dyestuffs mentioned in the lists on page 127, as suitable for wool, can be used successfully for silk dyeing. These colors have all been selected as unusually fast to light and, in this respect, are to be classified as “practically all of the first class,” i.e., as absolutely satisfactory against the action of sunlight. But, for a valuable and comparatively fragile material like silk, it is quite allowable to use colors for special shades which are less fast to sunlight, if they possess other valuable qualities. Such, for instance, are the two red dyestuffs, Fast Acid Eosine G (_Metz_) and Fast Acid Phloxine (_Metz_), which belong to the group of so-called Eosine or Fluoresceïn dyestuffs most of which, while very beautiful, are extremely fugitive. These two dyes, which give shades of pink and red with yellow and blue fluorescence, respectively, are considerably more fast than the rest of their group, and will rank in the third class, if not at the foot of the second class, as regards light-fastness. With regard to fastness to washing, it must be remembered that these Acid dyes are not fast at all, when dyed on silk in a broken soap bath. They may stand very light washing in a cold soap bath, but in boiling soapsuds will strip completely. This is important for the amateur, and indeed, for the professional dyer, for whom a dyed silk, either skein or in the piece, has come out unsatisfactorily—uneven or spotted, or too dark in shade—for it is possible, if the silk is of good quality, to clean off the color completely by boiling soapsuds, without injuring the goods. If the trouble is unevenness, while the shade is satisfactory, the color can be dissolved off in the boiling soap bath and then, on breaking the bath with a little acid, the same dye can be laid right on again, it is to be hoped this time in a satisfactory manner. The question of dyeing silk fast to washing, and also of dyeing silk black, will be dealt with in the next chapter. CHAPTER XII SILK—II BLACK DYEING OF SILK. WEIGHTING AND ADULTERATION OF SILK. DYEING SILK WITH COLORS FAST TO WASHING The dyeing process described in the last chapter, while well suited for dyeing silk bright and lustrous colors, is not so well adapted to dyeing it black. To be sure, there are several good fast acid blacks, such as Silk Patent Black, 2R, _Kalle_, or Neutral Wool Black, B, _Cassella_, or Cashmere Black, 3BN, _Elberfeld_, or Amido Black, 4024, _Metz_, which, dyed in full shades in a broken bath of soap or boiled-off liquor, will give fairly good results. But the best of these are not always quite satisfactory, the resulting color generally showing a tendency to be a deep full grey rather than a perfectly true lustrous black.