Textiles, for Commercial, Industrial, and Domestic Arts Schools / Also Adapted to Those Engaged in Wholesale and Retail Dry Goods, Wool, Cotton, and Dressmaker's Trades

by William H. Dooley

Logwood black-silk dyeing consists essentially of alternate dippings in separate baths with the mordant and dyestuffs suitable for producing the required color and weight. The number of dippings and the length of time taken in each operation depend on the intensity of the black wanted and the amount of weighting which is desired. The chief substances used for weighting are lead salts, catechu, iron, and nut-galls, with soap and oil to soften in some degree the harshness of the fabric which these minerals cause. As the details of the operations are practically the same for all kinds of logwood blacks (raven, jet, crape, dead black, etc.), the method for producing one will suffice for all. The process involves several distinct operations, as follows:

1. The Boiling Off. This is the removal of the gum and natural coloring matter in the silk. It is accomplished by boiling the skeins of silk in water and good olive oil soap for about one hour. This dissolves the gum and leaves the fiber clean and glossy.

2. Mordanting. This is done in a bath of nitrate of iron, in which the skeins of silk are allowed to remain one hour. The silk gains some in weight in this operation by absorbing a quantity of the iron in the bath. After having been dipped in the first bath three or four times, it is ready for the soap and iron bath, in which it is repeatedly immersed, the operation causing a deposit of iron-soap on the fiber which adds to its weight, but at the same time does not lessen its flexibility and softness. Eight dippings in the iron and soap bath increase the weight of the silk about 100 per cent.

3. Blue Bottoming. The next operation is to dye the silk blue, which is done by immersing it in a solution of potash. In this it is worked for half an hour, when it acquires a deep blue color. It is then taken out, and after rinsing is ready for the “weighting” operations.

4. “Weighting” Bath. A catechu bath is now prepared, in which the silk is entered and worked for an hour, and then allowed to steep over night. The result is that the blue on the silk is decomposed, and the goods by absorbing the tannin in the catechu increase in weight from 35 to 40 per cent. This bath is the most important one in the dyeing of “weighted” black silks, as the dyer can regulate the strength of the bath by the addition of tin crystals so as to increase the weight of the silk to an astonishing degree. The proportion of tin crystals used is regulated by the number of iron baths that have previously been given the silk; if two baths of iron have been given, 5 per cent of tin crystals are used; if four baths, 10 per cent, and so on. The action of these chemicals is somewhat complex. All that is known is that by reason of some peculiar quality possessed by silk it is enabled to combine with iron and tin, and that exposure to the air after the baths fixes these chemicals permanently upon the fibers, thus increasing their weight to almost any desired extent. Silk, according to its quality and weight, will take up of these substances from 50 to 200 per cent without creating much suspicion. Instances have been known in which silk has been increased nine times its own weight. All the operations thus far have had for their object the weighting of the silk, although the blueing and the catechu baths have some influence on the finished result. After these come the dyeing operations proper, two in number, mordanting and dyeing.

5. Mordanting. A bath of iron liquor heated to 130 degrees F. is provided. The silk is entered, worked well for one hour, then wrung out and hung up to “age” for two hours, after which it is ready for the logwood dye.

6. Dyeing. A bath of logwood liquor is prepared to which is added 10 per cent of fustic, and the solution is brought to a temperature of 150 degrees F. In this the silk is entered and worked for an hour, then taken out and wrung dry. Sometimes the black does not come up full enough, and in such cases the bath is repeated.

7. The final operation has for its object the restoration of the luster and suppleness of the silk, which has to some extent deteriorated from the many operations through which it has passed. The brightening and softening of the fiber are effected by immersing the silk in a bath of olive oil in the form of an emulsion. In this the silk is worked until it is thoroughly impregnated with the oil, when it is taken out and wrung dry, after which it is ready for the loom. Practically the same process is followed in piece dyeing, though only inferior grades of silk are dyed in the web.

Colored Silks. This class of silks is generally purer than black and sad-colored silks. It is not nearly so easy to weight the former as the latter, for the reason that there are but few substances capable of giving weight which do not interfere with the effect of light colored dyes. The weighting agents most generally used are sugar and acetate of lead. The weighting by sugar is done after the silk is dyed. A solution is made of pure lump sugar by placing it in a large copper pan with water and heating until dissolved. In this bath the silk is thoroughly saturated, and then dried and finished; or, the dipping process may be repeated several times if desired. One dipping will weight the silk about 12 per cent, two about 20 per cent, and three about 30 per cent. In a solution of acetate of lead, each dipping will weight the silk about 8 per cent, and these may be repeated as often as it is wished. In this case the weighting is generally done on the undyed, boiled-off silk, although it may be done on the dyed silk if the color is such as will stand the acid.

Mixed Silk Fabrics. Until lately silk was invariably dyed in the state of yarn. When the silk was to be woven into mixed fabrics, such as satin, gloria, etc., it was impossible to dye both fibers exactly the same shade. Formerly such fabrics were woven with the cotton and silk yarns dyed separately, care being taken to match them as closely as possible. The weaving of dyed yarns of different fibers is open to the objection that when the fabric comes to be finished there is a wide difference in the color, no matter how closely they may have matched in the beginning.