bleaching, shellac



bleaching, shellac defined in 1909 year

bleaching, shellac - Bleaching, Shellac;
bleaching, shellac -
  1. By exposure in thin threads to the atmosphere.
  2. 1 lb. of shellac is dissolved in 4 lb. of very strong alcohol, 1 lb. of bleaching powder - containing at least 20 per cent, bleaching chlorine - mixed into a paste with water, strained through linen, and the residue washed with water until the filtrate amounts to 1 lb. It is then mixed with a solution of carbonate of potash in 3 parts of water until no further precipitate is produced. The precipitate is separated by filtration, the warm alcoholic solution of shellac is treated with hydrochloric acid until the mixture is decidedly acid. The shellac then separates as white clots, which are to be washed until the water ceases to pass away milky, and then rolled out into thin strips upon a wet board.
  3. The shellac, previously broken into small pieces, is put into a flask, alcohol of 0.830 sp. gr. is poured upon it, and the whole is gently heated till the shellac is dissolved; next, so much coarsely powdered animal-charcoal is added to the solution that the whole forms thin paste; the flask is closed almost air-tight, and exposed to gentle heat (e.g. the sun); in 8 to 14 days it should have a light yellowish-brown colour, and yield a clear pure polish on light woods. It is then filtered through coarse blotting-paper, for which purpose it is well to employ a tin funnel with double sides. The portion which first passes through the filter may be preserved separately, and used as a ground or first polish. Then some more spirit is poured over the charcoal upon the filter, and the solution used as a last coating. Shellac purified by animal charcoal has a brown-yellow colour, but is perfectly clear and transparent; when diluted with alcohol, the colour is so slight that perfectly white wood may be polished with it.
  4. Boil and dissolve the shellac in a solution of carbonate of potash (pearlash), then pass chlorine through the solution. This bleaches and precipitates the shellac. Wash the shellac with water, then boil it in water until it is soft; roll it into a ball, then pull it into ropes as pulling gives a satiny appearance. Boiling with weak solutions of pearlash alone will remove colouring matter, and it can then be pulled as described.


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