Dyeing of SILK Black

Dyeing of SILK Black. To the general directions given under the article DYEING, n^o 17. we shall here add a particular receipt from Dr Lewis's Commerce of Arts. "The silk," says he, "washed as above directed *, is steeped in a decoction of one-third its weight of Aleppo or blue galls, or half its weight of the weaker white galls of Sicily and Romania, and afterwards washed with water; every 12 ounces are reduced by the cleansing to 9, which ought to be increased by the galling to 11, and no more. The dyeing liquor for 100 lb. of silk is prepared by boiling 20 pounds of galls in a sufficient quantity of water, (about 126 gallons), and adding to this decoction, after being settled and drawn off from the sediment, two pounds and an half of English vitriol, 12 pounds of iron-filings, and 20 pounds of the gum of the cherry or plum tree: that the gum may dissolve the more readily, it is put into a large copper cullender, immersed in the hot liquor, and stirred and worked from time to time with a wooden rod till it is all passed through. This mixture is kept for six or seven days or more, a circumstance supposed to be necessary for its perfection; and being then made as hot as the hand can bear, fresh parcels of the galled silks are dipped in it successively, and kept in about 10 minutes each. All of them, after being aired, are dipped again se-

veral times, with the addition of more vitriol and iron-filings, till they have acquired the requisite blackness, after which they are well washed in water."

This is the process which Mr Macquer tells us is followed in the manufactories at Tours and Genes; on which Dr Lewis makes the following remarks. Having repeated the process in small, with each of the articles exactly in the proportions above-mentioned, he found that it required 30 dippings, or more, to produce a good colour. With less than half this number the silk appears of a beautiful black when taken out of the liquor; but by washing, it becomes pale, and still more so by drying. The quantity of vitriol used, in all, was about eight times that recommended above to be added at one time, or one-fifth part of the weight of the silk; but the iron-filings put in at first remaining undissolved, it was not thought needful to add any more of this ingredient. The operation being repeated without iron-filings at all, no difference could be perceived between the two colours. Without the gum there was a very considerable difference in the silk as taken out of the dye; that which had been dyed with gum having a fine glossiness which the other wanted: the subsequent washing, however, destroyed that glossiness, so that the gum seemed to be of no service, but rather detriment, by thickening the liquor, and making it penetrate with more difficulty into the silk, in the same manner as it prevents ink from sinking into paper. Some silk dyed in the same manner as woollen cloth *, turned out a rusty black when the silk was put in white, but very good when the silk had been previously dyed blue.