Silk loses from twenty-five to twenty-eight per cent. of its weight in ungumming and whitening. The bags of silk should never be suffered to lie long together before they are emptied after being boiled, as their doing so would make the silk hard.
White silk, as before observed, is distinguished into five principal shades, namely, China white, India white, thread or milk white, silver white, and azure white.
The three first are prepared and boiled as has already been shewn. Silver and azure white in the preparation or ungumming thus: take fine powdered indigo, put it into water boiling hot, when settled the liquor is called azure.
To azure the silk it is taken from the ungumming copper after it is dressed and put into a trough of water; after it is worked, drained, and again dressed, it is ready for the
Whitening.
Put into a copper with thirty pails of water half a pound of soap; when it boils, and the soap dissolved, add for China white a little prepared annatto, (of which hereafter.) The silk, being on rods, is now to be put into the copper and kept turning end for end without intermission till the shade is uniform. For India white a little azure is added, to give the blue shade: for thread white and others a little azure is also to be added.
Observe, the liquor should be very hot, but not boiling; the turnings five times repeated, by which the shade is made even. When finished it is taken out, wrung, Spread on poles to dry, and that part of it required for sulphuring must be put upon rods or slight poles.
Sulphuring.
The hanks, being upon poles seven or eight feet from the ground, in an appropriate room, one pound and a half or two pounds of roll brimstone will sulphur a hundred weight of silk.
Put the brimstone, coarsely powdered, into an earthen pipkin with a little charcoal or small coal at bottom. Light one of the bits with a candle, which will kindle all the rest.