Shellac bleaching. simple recipes

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FACTORY TECHNOLOGIES AT HOME - SIMPLE RECIPES
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Shellac bleaching. Simple recipes and tips

Factory technologies - simple recipes

Directory / Factory technology at home - simple recipes

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Some varieties of varnishes require bleached shellac. Bleaching can be done by filtering an alcoholic solution of shellac through a bed of animal charcoal. This method has a significant drawback, which consists in the fact that part of the shellac disappears in the pores of the coal. A good way to bleach shellac is as follows.

5 kg of shellac is added to a boiling solution of 1,5 kg of soda in 25 liters of water. Heating is continued until the shellac is completely dissolved. Instead of boiling water, new water is added from time to time so that the amount of solution is constant.

Separately, a solution of bleaching powder is prepared, for which 30 kg of bleaching powder are dissolved in 17 liters of water. Lime is stirred and left to stand for several days. Then the clear solution is drained from the white lime precipitate and a saturated soda solution is added to the clear solution. Soda must be added until the addition of new portions stops the precipitation (calcium salt), after which the clear solution is drained and the shellac soda solution is added to it.

A solution of shellac with a bleaching solution is left to stand open in the air until it is completely discolored. Then a 20% sulfuric acid solution is added to the colorless solution until the colorless shellac stops settling. The settled bleached shellac is removed and dried.

According to the Austrian method, shellac is bleached with chlorine gas diluted with a tenfold volume of air, water vapor or some other indifferent gas. Shellac is dissolved in a soda solution through which chlorine is passed, which produces bleaching.

With this method, care must be taken that the solution is always alkaline, since otherwise the resulting hydrochloric acid will cause shellac to fall out. The resulting hypochlorous acid is the bleaching agent. In practice, bleaching is carried out as follows.

Dissolve approximately 5 kg of raw shellac in 100 liters of boiling water with 750 g of soda. Into this solution at constant; diluted chlorine gas is passed through while stirring. After slowly passing about 1 kg of chlorine gas, bleaching is complete. If diluted chlorine is introduced into an alcoholic shellac solution, then it acts directly, and the end of bleaching is recognized by the desired light color of the shellac.

From this solution, bleached shellac is obtained by evaporating the solvent in a vacuum, since when the alcohol is distilled off under atmospheric pressure, the shellac becomes dark again.

Author: Korolev V.A.

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