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Coloring Finishing And Painting Wood
Wood bleaching is often very successfully accomplished by use of an application of a solution of potassium permanganate followed before the first coating dries by a solution of sodium bisulphite. The following formula indicates the best strength of chemicals for use:
Solution No. 1
1 ounce potassium permanganate (other amounts may be use
Solution No. 2
3 ounces sodium bisulphite (4 ounces for stronsr bleach)
1 gallon water (distilled preferred)
Allow the mixture sufficient time for cooling before use.
The permanganate solution should be applied very freely with a brush. If the wood be allowed to dry, it will be of a slight purple tint, which will fade out with other bleaches. It is best, however, to apply Solution No. 2 before the first solution dries. The sodium bisulphite solution seems to cause a bleaching out of all dark-colored pigments and to produce a whitening or bleaching of almost any wood, tho the final tone or color varies with different woods.
The combination of an application of permanganate of potassium solution followed by a wash or coating of sodium bisulphite has proved to be a very powerful bleaching agent for wood. After the desired color has been obtained, it is best to sponge the wood with clean water to remove any excess of bleaching chemicals.
Sometimes a solution of sodium hyposulphite in a strength of 2 to 4 ounces to the gallon of hot water is substituted for the No. 2 solution of sodium bisulphite. The bleaching results of both of these chemicals are similar when used in a second solution. The hyposulphite should not be used without a previous treatment with potassium permanganate solution because it is ineffective.
347. Other Bleaching- Agents.—It is possible to bleach wood with several other chemicals which are mostly alkaline, or used with an alkali, or following the application of one. The best known and most affective of these bleaches for present-day use are peroxide of hydrogen (H2O2) and lime bleaching powders.
Hydrogen peroxide is an effective but rather expensive bleaching agent, which is sometimes used for small jobs and for bleaching stains. Before application of hydrogen peroxide a wash coat of ammonia or dilute sodium hydroxide should be placed on the wood. Then the bleaching agent, hydrogen peroxide, may be brushed onto the wood several times in full strength, if necessary, in order to obtain whiteness in the wood being treated. The wood seems to darken at first, then the dark-colored extract or pigment is bleached, possibly by oxidation of products soluble in water. If the hydrogen peroxide be fresh and strong, a 30% solution with water is often enough. It is best to wear rubber gloves and to wash off with water if any hydrogen peroxide comes in contact with the skin.
