The dyeing process



The art of dyeing has for its object the fixing permanently of a color of a definite shade upon stuffs. The stuffs are animal, as silk wool, and feathers, or vegetable, as cotton and linen. The former take the colors much more readily, and they are more brilliant.

In some cases, as in dyeing silk and wool with coaltar colors, the color at once unites with the fiber; generally, however, a process of preparation is necessary. In certain other cases, as in dyeing silk and wool yellow by nitric acid, the color is due to a change in the stuff, and is not properly dyeing.

Insoluble colors are managed by taking advantage of known chemical changes; thus chromate of lead (chrome yellow) is precipitated by dipping the stuff into solutions, first of acetate of lead, and then of bichromate of potassa.

Mordants (bindermittle, middle binder of the Germans) are bodies which, by their attraction for organic matter, adhere to the fibre of the stuff, and also to the coloring matter. They are applied first, but in domestic dyeing they are often mixed with the dye-stuff. By the use of a mordant, a dye which would wash out is rendered permanent.

Some mordants modify the color; thus alum brightens madder, giving a light-red, while iron darkens it, giving a purple.

_MORDANTS._

The principal mordants are alum, cubic-alum, acetate of alumina, protochloride of tin, bichloride of tin, sulphate of iron, acetate of iron, tannin, stannate of soda.

_DYE-STUFFS._

The materials used in dyeing are numerous; the following are the most important: Madder, indigo, logwood, quercitron, or oak-bark, Brazil wood, sumach, galls, weld, annato, turmeric, alkanet, red launders, litmus or archil, cudbear, cochineal, lac; and the following mineral substances: ferrocyanide of potassium, bichromate of potash, cream of tartar, lime-water, and verdigris.

_Coal-tar Colors._

Are made under patents, and on the large scale. The receipts for their manufacture will, therefore, not be given; in many cases, indeed, they are kept secret. Especial instructions as to their use will be found at the end of the article.

_Other Materials._

A bath of cow's dung is used after mordanting vegetable fibres, to remove the excess of mordant. A solution of silicate of soda has been lately used as a substitute.

Albumen, or gluten, is used to thicken the colors for printing, and sometimes to fix them. The colors are incorporated with the albumen applied to the stuff. By exposure to heat the albumen is coagulated and the color fixed.

_Silicate of Soda, as a Means of Fixing Mordants._

The use of silicate of soda in calico printing has the advantage of rendering the colors deeper than when the dung-bath alone is used. In reference to the action of this salt, it is worthy of remark that alkaline silicates exist in cow-dung, which according to Rogers, contains 17.5 per cent. of solid substance, 15 per cent. of this ash; so that the fresh dung contains 2.6 per cent. of ash, and the ash contains 62.5 per cent. of silica. A large portion of this silica is in the insoluble condition, but the quantity of soluble silica is not inconsiderable. The soluble portion of the ash amounts to 38 per cent., and of this 12 per. cent. is silica, and 10 per cent. potash and soda. There is, therefore, reason for regarding silicate of soda as the efficient ingredient of cow-dung.

_Alum._

Used as mordant for silk and wool, is then dissolved in water. If it contain iron, reds will be injured. It is a sulphate of alumina combined with sulphate of potassa or ammonia. The alumina is the active mordant. Ammonia alum may be distinguished from potash alum by adding a little caustic potash to the powder; if ammonia exist it will be given off, and may be easily recognized by its pungent smell.

_Cubic Alum_

Is much used. It is made by adding carbonate of soda to alum until the precipitate, at first thrown down, is redissolved. If too much be added a permanent precipitate will be formed. It yields its alumina much more readily to organic matter than common alum.

_Acetate of Alumina._

Used for COTTON and LINEN. When heated the acetic acid is driven off, and the alumina remains in the fibre. It is made by adding a solution of acetate (sugar) of lead to a solution of alum as long as any precipitate is formed, or take 8 1/2 lbs. alum, 6 1/4 lbs. sugar of lead; dissolve each in 2 galls. of boiling water. Mix and allow to settle.

_Bichloride of Tin (Salt of Tin, Nitromuriate of Tin)._

Take 4 lbs. of commercial nitric acid, 1/2 lb. sal ammoniac; put it in a stone vessel, and add 1/2 lb. of pure granulated tin, or dissolve granulated tin in a mixture of 2 parts muriatic to 1 of nitric acid as long as any is taken up.

_Protochloride of Tin._

Dissolve granulated tin in hot muriatic acid as long as any is taken up. Cream of tarter is generally added to the alum and tin bath.

_Copperas._

Used for dyeing dark shades in wool. It is made by dissolving clean iron in dilute sulphuric acid and crystallizing. An inferior kind is made from pyrites. It contains iron in the forte of protoxide. On exposure to the air, however, more oxygen is taken up, and, as in the case of all the salts of the protoxide of iron, sesquioxide is formed. This is a powerful mordant, as may be seen by the tenacity with which iron mould adheres to stuffs.

_Acetate of Iron._

Is made by dissolving iron scraps in acetic or pyroligneous acid. It is preferred for dyeing vegetable fibres.

_Nitrate of Iron._

Take 10 1/4 lbs. each nitric and muriatic acids, and add little by little 72 1/2 lbs. of copperas dissolved in water.

_Preperation for Dyeing._

Wool requires to be scoured; raw silk to be ungummed; cotton to be sheared, singed, and bleached. (See BLEACHING AND SCOURING.)

_To Determine the Effects of Various Salts or Mordants on Colors._

_The Dye of Madder,_

For a madder red on woolens, the best quantity of madder is 1/2 of the weight of the woollens that are to be dyed, the best proportion of salts to be used, is 5 parts of alum and 1 of red tartar, for 16 parts of the stuff.

A variation in the proportions of the salts, wholly alters the color that the madder naturally gives. If the alum is lessened, and the tartar increased, the dye proves a red cinnamon. If the alum be entirely omitted, the red wholly disappears, and a durable tawny cinnamon is produced.

If woollens are boiled in weak pearlash and water, the greater part of the color is destroyed. A solution of soap discharges part of the color, and leaves the remaining more beautiful.

Volatile alkalies heighten the red color of the madder, but they make the dye fugitive.





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