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Coloring Finishing And Painting Wood
Bleaching, which means a whitening or loss of color, has been known in some of its forms for ages. Bleaches have been used to whiten various materials, particularly cloth fibres and paper pulp, oils of several kinds, and bees' wax.
Very slow but effective means of bleaching textiles have been known for centuries. The historians do not seem to have recorded the procedures used in antiquity by the Phoenicians, Egyptians, Greeks, and Romans. After the Crusades, the Dutch became the bleachers of Europe and retained leadership in the art of bleaching until the latter part of the 18th century. Then, in England, a much more rapid process than the old one of alkaline lyes, washing, and sunning employed by the Dutch came into use thru the substitution of dilute sulphuric acid. The new process brought greatly increased speed in bleaching. The use of chlorine came in England about 1787. It was.introduced by Scheele alter a suggestion by James "Watt.
The modern methods of bleaching wood are similar to those used in whitening textiles. Different processes have been found best for the various fibres such as cotton, linen, wool, and silk. Some of the same bleaching materials are now used for bleaching wood.
346. Bleaching Agents Used on Wood.—Oxalic acid was formerly the bleaching agent usually recommended for bleaching wood. A solution for bleaching may be prepared by use of about 10 to 16 ounces of the white crystalline powder to a gallon of quite hot water. The bleaching solution is poisonous and should be kept in glass or earthen jars. Its bleaching reaction on wood is rather weak, and the dust from sanding wood treated for bleaching is dangerous to breathe. The acid should be washed off and the bleached surfaces allowed to dry. Washing removes most of the danger from inhaling poisonous dust while sanding. For safety, if much sanding is to be done, about 3 or 4 ounces of borax should be dissolved in hot water and brushed on the wood to neutralize the poisonous acid. A dust mask or wet sponge may be worn over the nose if any large job of sanding is to be done after bleaching with oxalic acid.
Experience indicates that an oxalic solution is most effective if applied hot in two or three coats, and then a No. 2 solution of hyposulphite soda in a strength of 1 ounce of "hypo" to 12 ounces of hot water should be applied. These bleaching agents are usually spread with a rubber-set, flat wall brush. The borax solution mentioned above should be the third and final wash—given to neutralize the other chemicals.
Two-solution bleaches of another type which have alkaline rather than acid reactions are now quite generally used and are sometimes similar to some of the bleaching agents commonly used for wool. At present two-solution bleaching materials are considered to be the most powerful agents for removing color and, on the whole, the most effective, the cheapest, and the most practical.
