122

DYEING.

The properties of hematine explain the mode of using logwood. When stuffs aredyed in the infusion or decoction of this wood, under the influence of a base which actsupon the hematine in the manner of an alkali, a blue dye, bordering upon violet, isobtained. Such is the process for dyeing cotton and wool a logwood blue by means ofverdigris, crystallized acetate of copper, and acetate of alumina.

When we dye a stuff yellow, red, or orange, we have always bright tints; with blue,we may have a very dark shade, but somewhat violet; the proper black can be'obtainedonly by using the three colors, blue, red, and yellow, in proper proportions. Hence wecan explain how the tints of yellow, red, orange, blue, green, and violet, may be browned,by applying to them one or two colors which along with themselves would produceblack ; and also we may explain the nature of that variety of blacks and grays whichseems to be indefinite. Nutgalls and sulphate of iron, so frequently employed for theblack dye, give only a violet or bluish gray. The pyrolignite of iron, which containsa brown empyreumatic matter, gives to stuffs a brown tint, bordering upon greenishyellow in the pale hues, and to chestnut brown in the dark ones. By galling cottonand silk, and giving them a bath of pyrolignite of iron, we may, after some alterna-tions, dye them black, flails, logwood, and a salt of iron, produce merely a very deepviolet blue; but by boiling and exposure to air, the hematate of iron is changed, becom-ing red-brown, and favors the production of black. Galls and salts of copper dye stuffsan olive drab, logwood and salts of copper, a violet blue; hence their combination shouldproduce a black. In using sumach as a substitute for galls, we should take into accountthe proportion of yellow matter it contains. When the best possible black is wantedupon wool, we must give the stuff a foundation of indigo, then pass it into a bath of log-wood, sumach, and proto-sulphate of iron. The sumach may be replaced by one third ofits weight of nutgalls.

8. Of dyed stuffs considered in reference to the fastness of their colors, when exposedto water, light, heat, air, oxygen, boiling, and reagents.

Pure water without air has no action upon any properly dyed stuff.

Heat favors the action of certain oxygenized bodies upon the carbonaceous and hydro-genous constituents of the stuff; as is seen with regard to chromic acid, and peroxyde ofmansanese upon cotton goods. It promotes the solvent action of water, and it even affectssome colors. Thus Prussian blue applied to silk, is reduced to peroxyde of iron by longboiling.

Light without contact of air affects very few dyes.

Oxygen, especially in the nascent state, is very powerful upon dyes. See Bleaching.

The atmosphere in a somewhat moist state affects many dyes, at an elevated tem-perature. Silk dyed pink, with safflower, when heated to 400° F., becomes of a dirtywhite hue in the course of an hour. The violet of logwood upon alumed wool becomesof a dull brown at the same temperature in the same time. But both stand a heat oi300° F. Brazil red dye, turmeric, and weld yellow dyes, display the same phenomena.These facts show the great fixity of colors commonly deemed tender. The stun 8become affected to a certain degree, under the same circumstances as the dyes. Thealterabiliiy even of indigo in the air is shown in the wearing of pale blue clothes; mthe dark blue cloth there is such a body of color, that it resists proportionally l° n g eI 7but the seams of coats exhibit the effect very distinctly. In silk window curtains, whinhave been long exposed to the air and light, the stuff' is found to be decomposed, as we

as the color. • t d in

Boiling was formerly prescribed in France as a test of fast dyes. It consistedputting a sample of the dyed goods in boiling water, holding in solution a determin ^quantity of alum, tartar, soap, and vinegar, &c. Dufay improved that barbarousHe considered that fast-dyed cloth could be recognised by resisting an exposure of twhours to the sunshine of summer, and to the midnight dews; or of sixteen daywinter.

In trying the stability of dyes, we may offer the following rules:— worn

That every stuff should be exposed to the light and air; if it be intended to beabroad, it should be exposed also to the wind and rain; that carpets, moreover, slio ^subjected to friction and pulling, to prove their tenacity; and that cloths to beshould be exposed to the action of hot water and soap.

In examining a piece of dyed cotton goods, we may proceed as follows: ^oil-

Suppose its color to be orange-brown. We find first that it imparts no color so lutioning water; that protochloride of tin takes out its color; that plunged into a leavesof ferroprussiate of potash it becomes blue ; and that a piece of it being burneu, tte r isa residuum of peroxyde of iron; we may thence conclude that the dyeingperoxyde of iron. . or with

Suppose we have a blue stuff which may have been dyed either with jn . - frst intoPrussian blue , and we wish to know what it will become in use. We in< l’" re bv iti ifthe nature of the blue. Hot water slightly alkaline will be colored blue j