Dyeing Wild Silks.—It has been found difficult to handle satisfactorily the different sorts of wild silks in the factory. The bleaching of them has been very troublesome, although of late years the problem has been solved pretty well. And the ordinary process for dyeing silk with Acid dyes in a broken soap, or boiled-off liquor, bath is, for full deep shades at any rate, not always satisfactory. In consequence most of the genuine pongee or Shantung cloth is sold in the natural unbleached color, a pleasant shade of tan, or else in light shades.
Perhaps the best results in dyeing pongee silk full, deep, even shades are obtained by mordanting the material with tannin and tartar emetic, just as cotton is mordanted before dyeing it with Basic colors, and then using in the dye-bath one or the other of the so-called “Janus” colors,—a group of colors on the border line between Basic and Acid, of which the best are Janus Yellow G, Janus Yellow R, Janus Red B, and Janus Black 1 (Metz).
This process, however, is too complicated for the unprofessional dyer to use with much success.
For all but the very full shades the craftsman is advised to use the Acid colors, as, for instance, some of the selected colors of the different houses, listed in Chapter VII, in a bath acidified with acetic acid, and without the use of soap.
For dark dull shades the Sulphur colors can be used, especially if some care is taken to reduce the alkalinity of the bath by neutralizing or nearly neutralizing the sodium sulphide with a little acid sodium sulphite. If the desired shade is so dark as to necessitate heating and dye-bath, it is also advisable to add a little gelatin.
For full shades of rather brighter quality the Vat dyes may be employed, also with precautions against the tendering action of the caustic alkali upon the fibre.
Before, however, starting in to dye a piece of pongee on the assumption that it is made from tussah silk, it is very advisable to examine it carefully, picking out the individual threads and untwisting them, and to make a few dyeing tests upon small samples. For a large proportion of so-called pongee, which in color, lustre, feel, and general appearance resembles the genuine Shantung very closely, is simply made from spun or waste silk, and can be dyed like ordinary silk.
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.