658

DYEING AND CALICO PRINTING.

with the exception of a few non-metallic green and pink shades, permanent.Butterflies and moths, on the other hand, no matter how thoroughly protectedagainst air, fridtion, or other mechanical injury, have their colours completelydischarged in the course of a few years even by diffused daylight. Greens,lilacs, and pinks are here, again, the most fugitive, whilst yellows, browns,full reds, and all “ metallic” or iridescent spots resist longest.

Whatever diversity of opinion may prevail concerning the part played bylight in the development of colours and in their fixation upon tissues, therecan be no doubt as to its influence when once the process of dyeing, printing,or painting is completed. In almost every case it is injurious. The adtionranges from rapid destruction, as in the case of safflower pinks, magentas, &c.,to gradual deterioration, as with royal blues, chrome blacks, &c. Few colours,indeed, do not show a distinction if a swatch be cut in halves and preserved,the one in darkness and the other in the light.

Nor is this action confined to dyed or printed tissues. The colours them-selves, be they dyes or pigments, are also affected by exposure to light.Extract of indigo, if exposed to diffused daylight, gradually loses its bluecolour, and is reduced to a faint yellowish green. Mordants also, especiallythe preparations of iron and tin, lose their affinity for the fibre, and arerendered worthless by even a short exposure to direct sunlight. This changeis very marked with the mordant known as nitrate of tin or “bowl-spirits”(see p. 527). By sunshine it is rendered milky and turbid, a great part of thetin in solution is precipitated, and the remainder becomes useless. Cotton orwoollen fibre worked in this spoiled mordant and then transferred to the dye-beck, takes only very flat, meagre, and uneven shades. The ordinary per-salts of tin (crimson spirit, oxymuriate, &c.) are little changed in appearanceby the adtion of light, but they do net work on the fibre, the shades ultimatelyproduced closely resembling those obtained with a spirit which has been“fired” (see p. 529). This is not the only case in which the effedts of lightin dyeing processes agree with those of an elevated temperature. Safflowershades are discharged if dried in too great a heat, far below a temperatureinjurious to the fibre, just as readily as if exposed to diredt sunlight.

Nitrate of iron, especially if intended for dyeing royal blues, should be keptin the dark until wanted. If this precaution is negledted the mordant becomesturbid, and the shades produced on the fibre are deficient in bloom andbrilliance. This result is the more interesting, because solutions of ironintended for use in the manufadture of Prussian blue as a pigment are notinjured by the sun’s rays. Some practical colour makers, indeed, contendthat the beauty of the pigment is improved if the materials are exposed tolight previous to precipitation.

Light is supposed to have an adtion upon madder from the time when thedried root is ground up and packed very finely in strong casks. The oldermanufadturers, especially in Zealand and Alsace, have from time almostimmemorial considered that madder, while being ground and packed, shouldbe withdrawn entirely from daylight. The custom of the Meestovcn, as thedrying and grinding establishments are called in Zealand, was to work byscanty lamplight. In modern times this precaution has been laid aside andthe root is generally ground by daylight. There are, however, some personspossessing great pradtical acquaintance with madder (especially in Zealand)who maintain that the root ground in the dark is better—works better in the