DYEING SILK WITH COLORS FAST TO WASHING
As a rule the method previously described of dyeing silk with Acid dyes in a broken bath of soap, or better, of boiled-off liquor, will be found perfectly satisfactory. The shades are easily obtained, the colors are brilliant, and, if the right dyes are used, exceedingly fast to light, and the material, if properly rinsed, suffers no deterioration.
On the other hand these colors are not, in the slightest degree, fast to washing.
The dyed goods can be cleaned with gasoline and the like, but when passed through a lukewarm bath of soap and water they bleed badly, and in boiling soapsuds the color can be completely stripped from them.
In most cases this is not a serious objection, for a person who will send a handsome hand-dyed silk scarf or piece of embroidery to the family washtub is entitled to scant sympathy if the results are disastrous. But occasionally it is important to have colors on silk which can be guaranteed against moderate or even against, severe, washing.
Fast Colors on Silk.—There are two grades of fastness known to the dyers—“fast” and “embroidery fast.”
“Fast” means simply that the silk is to be dyed fast to ordinary, careful handling so that the colors will not bleed or run in a warm or even hot soap bath, but does not guarantee them against every possible maltreatment.
The best way of doing this is by the use of the Direct Cotton or Salt dyes, described in Chapter III, which, it will be remembered, only dye wool or silk at a high temperature, at or near the boiling point and, preferably, in an acid bath, but, when once on, are very hard to dislodge. The selected ones are very fast to light and present a great range of bright, attractive colors, which are nearly, if not quite, as brilliant as those produced by the Acid dyes.
They are applied in a boiling bath containing a little acetic acid, and a good deal of salt, especially for full shades. For lighter shades, the presence of salt is hardly necessary. The goods are to be finished just as with the Acid dyes, with a soap bath followed, if the scroop is desired, by a weak bath of acetic acid.
The results, when carefully done, are very good. They possess, however, one disadvantage for the amateur dyer. These colors are quite hard to strip, and so, the desired effect must be produced the first time, or not at all. It is not possible to strip an unsatisfactory shade in a hot soap bath, and dye it over and over again without injury, as in the case with Acid dyes. They are best stripped by soaking in a bath of sodium hydrosulphite, and then washing.
Embroidery Fast Colors.—While the above process gives shades fast enough against all ordinary washing, it sometimes happens that silk must be dyed fast enough to withstand exactly the same treatment that coarse cotton or linen goods are subjected to, without bleeding or staining. The salt dyes are not quite fast enough for this, particularly because, not having been converted in the dyeing process into a special insoluble condition, if they should be detached from the fibre by strong or hot soaping, they would be liable to stain the neighboring tissues and not wash off quite clear.
One of the hardest tests that colored silk is called upon to stand is when, in small quantities, it is used with a large amount of white linen or cotton goods. Thus, for instance, when monograms are embroidered in red or blue silk upon white towels or napkins, and the latter are scrubbed, week after week, in the regular wash, the color must be fast, indeed, not to show some evidences of running. Hence the term “embroidery fastness” as applied to this class of dyes. Thanks, also, to the amiable practice of the modern laundress of lightening her labors by the addition of bleaching powder and other strong chemicals to the washtub, it is very important that a silk dyed “embroidery fast” should be able to withstand the action of these agents as well as of soap. Up to the last few years these colors were only obtained by the use of the Alizarine dyestuffs, the full rich scarlet so often used for this purpose being the modern form of the old, madder-dyed, Turkey red of our forefathers.
But, during the last few years, the troublesome and tedious mordanting processes necessary for the proper development of color by the Alizarine dyes, have been replaced, for craftsmen, and, indeed, by most professional dyers, by the much simpler and shorter processes of vat dyeing. As long as Indigo was the sole representative of the class, it was of very little use for silk dyeing. But since the introduction of the splendid series of new vat dyes, the Algol, Ciba, Helindone, Indanthrene, and Thio Indigo colors, which, dyed in a single bath, give a whole range of brilliant shades, wonderfully fast to light and to washing, the necessity for mordant colors has very largely disappeared.