Dyeing Silks

Scientific American 11, 11.9.1869

Written for the Scientific American by Dr. M. Reimann, of Berlin.

Preparation of the Raw Silk Previous to Dyeing.

Supposing it is required to dye 100 lbs. of raw silk, 12 lbs. of soap are boiled with a sufficient quantity of river or rain water until all the soap is dissolved; the water is then allowed to cool a little and the silk is introduced; it is allowed to remain in the solution of soap 1½ hours, the liquid in the meantime being kept at the boiling temperature. The silk is then wrung dry, put into linen bags, and once more introduced into a solution of 12 lbs. of soap. It is once more boiled for 1½ hours, and finally washed in the river.

Preparation of Second-Hand Silk Stuffs.

The silk is cleaned in a warm solution of carbonate of soda, then boiled for an hour and a half in a soap bath, and washed in the river. It is next placed in water acidulated with a little sulphuric acid, and suffered to remain in it until the original color has wholly disappeared. It is then washed finally in the river.

To Dye Silk Blue.

The silk is immersed for some time in a solution of alum, which served as the mordant. Meantime a solution of indigo carmine in boiling water is mixed with warm water in a suitable vessel. In order to dye 10 lbs. of silk ¾(?) lb. of indigo is requisite. The silk is immersed in this bath until the requisite shade is obtained. It is then wrung out and allowed to dry in the shade.

In order to give a deeper tint to the material, the silk is passed through an indigo vat. In this way the deepest tints may ho obtained.

To Dye Silk Greenish Blue.

In order to dye 10 lbs. of silk, 1 lb. of alum is dissolved in a sufficient quantity of water to completely cover the silk; ½oz. of sulphuric acid is then added, and the silk is allowed to remain 4 hours in the bath. It. is then taken out and wrung dry. A solution of ½ or ¾ lb. of indigo carmine in warm water is then added to the alum bath, well mixed by stirring, and the silk once more introduced. It is suffered to remain in the dyeing bath until a sufficiently dark shade has been obtained. It is then taken out, wrung out, dried, and complettxl. In order to obtain a uniform color the indigo is gradually introduced into the bath.

A Reddish-Blue Dye.

In order to dye 10 lbs. of silk ¼ lb. of protochloride of tin is dissolved in water, and to this solution are added 2 lbs. of solution of nitrate of iron and 1 oz. of sulphuric acid. The mixture is allowed to stand a day and the clear portion of the liquid is then poured into a sufficient quantity of water. The silk is submitted to the action of the mordant thus obtained for half an hour. It is then wrung out, washed in river water, and finally dyed in a bath containing 2/3 lb. of yellow prussiate of potash and ¼ lb. of sulphuric acid.

The dyeing operation should continue a quarter of an hour. The silk is wrung out, introduced once more into the mordant bath, then dyed as before, and so on until the shade obtained is dark enough. When this is the case the silk is washed, dried, and finished.

Yellow Dye by Means of Weld.

In order to dye 10 lbs. of silk, 3 or 4 lbs. of weld are boiled in water for 20 minutes; the decoction is then filtered through linen and suffered to cool a little. The silk is then boiled as before with one fifth of its weight of soap, then allowed to remain some time in an alum bath, and finally introduced into the above-mentioned weld decoction. Here it is worked about until it is uniformly dyed. A little carbonate of potash may be added to the weld bath in order to vary the shade a little. The yellow tint obtained from weld is sufficiently deep.

Yellow Dye by Means of Quercitron.

In order to dye 10 lbs. el silk, 5 lbs. of quercitron bark are boiled with a sufficient quantity of water; the clear decoction is then poured off, and the silk previously mordanted by alum is immersed in it for half an hour and then washed. By varying the amount of quercitron and adding crystals of soda, various shades of yellow may bo obtained.

It is a good plan to add some gelatine to the decoction of quercitron before making use of it, as in this way the tannic acid contained in the quercitron bark may be removed from the liquid.

Brimstone Color by Means of Picrid Acid.

Picric acid is very often employed at the present day to give a light yellow tint to silk. With regard to the nature of picric acid, it is one of the products obtained from coal tar.

Among the products obtained by the distillation of coal tar at a temperature varying from 150° to 190° Centigrade, is an oil which contains a considerable quantity of carbolic acid.

The benzoic, being the hydride of phenyl C₁₂H₅H, phenyl the carbolic acid is the alcohol C₁₂H₅ O+HO, but is indued with acid properties.

On treating the oil containing carbolic or phenic acid with solution of soda, decanting the clear solution of phenylate of soda and adding sulphuric acid to it, an oil is obtained which when distilled and dried, furnishes crystals of pure phenic acid. This substance, when heated with nitric acid, readily furnishes products in which hydrogen is replaced by the complex atom NO, or subnitric acid.

On heating phonic acid with three equivalents of nitric acid, a product is obtained in which three equivalents of NO, have taken the place of three equivalents of H, thus
C₁₂H₃O+HO+8NO₅=C₁₂H₂O+HO+8HO(NO₄)₃

The whole mass has the appearance of a yellow crystalline paste, which, on being dissolved in boiling water and recrystallized, furnishes yellow crystals to which chemists have applied the name "trinitrophenic acid." In commerce it is called "picric acid," "Welter's bitter," and "picronitric acid."

In a state of purity it is a yellow crystalline substance, having a very bitter taste, and soluble in cold water, which has a brimstone yellow tint when holding this substance in solution. All animal substances when dipped in this solution of picric acid are dyed yellow. Therefore, the the silk has only to be introduced into a solution of the acid containing tor every 10 lbs. of silk to be dyed 2 ozs. of picric acid, when a fine brimstone shade will be readily obtained.

The color easily resists the action of sunlight and of air but readily disappears on washing with soap or even with clean water. Therefore the silk must never be washed after dyeing, but merely dyed in the solution and then finished.

The yellow color produced by picric acid may be easily discovered by applying the tongue to the dyed article. The exceedingly bitter taste is a satisfactory proof that picric acid is deposited on the fibers.

Yellow Dye Produced by Annatto.

In order to dye 10 lbs. of silk, 1/8(?) lb. of annotto is boiled for half an hour with a solution of ¼ lb. of carbonate of potash and a sufficient quantity of water. The silk is introduced into this bath and well worked about, while the temperature of the bath is kept close upon the boiling point, though never actually boiling. The requisite shade having been obtained, the silk is washed, then heated at 40° or 50° Centigrade with alum, in the solution of which it is allowed to remain a night. In the morning it is again washed and dyed a second time in a bath at a temperature of 30° Centigrade, which contains a decoction of weld and a quantity of the soap used before for the purpose of cleaning the silk. The dyeing operation is effected by passing the silk seven times through the bath.

The above-mentioned weld decoction is prepared by boiling 20 lbs. of weld with 10 gallons of water and lb. of carbonate of potash. The silk, when sufficiently dyed, is passed through a soap bath containing 8 lbs. of white soap.

An Orange Dye.

In order to impart an orange tint to 10 lbs. of silk, 1 lb. of annotto and 3 lbs. of carbonate of soda are boiled with water. The solution thus obtained is filtered and the silk worked about in it for half an hour. It is then wrung out, washed in the river, dried, and finished.

A Black Dye.

This most important color is obtained as follows;

1. Blueish-Black.

To dye 10 lbs. of silk blueish-black 21bs. of alum are dissolved in 20 lbs. of boiling water. This solution is then added to a sufficient quantity of cold water. The silk is then introduced, worked about some time, and allowed three hours in the solution. Meantime 2/8 lb. of sulphate of iron is dissolved in water, and the solution added to a bath of warm water, and the silk, removed from the alum bath, is introduced into it. It is worked about here for a quarter of an hour and then washed.

The dyeing bath is prepared as follows:
Five pounds of logwood in powder or small chips emplaced in a bag and boiled in water until all the coloring matter is extracted. The bag with the wood is then removed from the water, and a decoction added consisting of 2/3 lb. of barrel soap in water. Having added the needful quantity of water, and varied the temperature of the bath so that the hand can be put into it without injury, the silk is introduced and worked about in it for twenty minutes. It is then washed and finished. If the color is still not dark enough the silk must be immersed in a fresh logwood bath.