This section is from the "A Complete Dictionary of Dry Goods" book, by George S. Cole. Also available from Amazon: A complete dictionary of dry goods and history of silk, cotton, linen, wool and other fibrous substances,: Including a full explanation of the modern processes ... together with various useful tables.
Scouring. - Up to this time the silk fiber continues to be lustreless, stiff, and harsh, from the coating of gum on its surface. The removal of this gum is performed by the operation of boiling-off or scouring. To boil off, say 300 pounds of thrown silk, about 60 pounds of white soap is shred and dissolved in 200 gallons of pure water, at a heat of 195 degrees. In this the hanks of silk are immersed, being continually turned around so as to expose all portions equally to the solvent influence of the hot solution. For some purposes—making gauze, crape, etc. - the silk is not scoured; and for dyeing certain colors, half-scouring is practiced. The perfect scouring of French silks removes 25 per cent, of their weight, while China silks lose 30 per cent. Silks to be finished white are bleached by exposure in a closed room to the fumes of burning sulphur, and afterward washed in pure cold water to remove all traces of the sulphur.