Bleaching Wood, How to Bleach Wood
Introduction to wood bleaching solutions, how to bleach wood.
¶ The wood finisher has occasion to use homemade bleaching solutions for the purpose of removing stains from woods to be finished or refinished, such as rust stains, water and weather stains. He also needs a bleaching solution occasionally to bleach large surfaces of maple, birch, oak, walnut and other woods which are to be finished in as light a color as possible, for instance, oak, which is to be finished with one of the popular light gray, two-tone finishes with white filler, and walnut or gum, which are to be finished with the very light brown French walnut color. Then again when old stained and varnished surfaces are stripped off, removing all the old finish possible the wood is sometimes found to be too dark to take the new stain of light color and make a nice job. Then bleaching is resorted to.
¶ The bleaching processes use water solutions and they raise the grain of the wood. So after the bleaching and neutralizing washes the surface is permitted to dry and is then sandpapered to cut off the raised wood fibres. Sometimes a very thin coat of white shellac is brushed on to make the wood fibres stiff so they can be clipped off easily with the sandpaper. This coat of shellac should be about a 2-lb. cut, that is, 2 lbs. of white bleached gum shellac to 1 gallon of denatured alcohol.
¶ After bleaching the surface may contain a bit of the chemicals and it is well therefore to wash up immediately with clean water, using a sponge. Then a coat of ordinary table vinegar without dilution will neutralize any alkaline traces left on the surface and make it safe for finishing coats. The surface should be allowed to dry at least twelve hours before the finishing coats are put on.
¶ There are many chemical solutions used for bleaching. Some are most effective on one wood while others succeed best for other woods. The oxalic acid solutions are probably used most by wood finishers in the house building industry.
¶ Before using any bleaching solution it is best to thoroughly clean and scrub a surface, using hot water to which soap and a little sal soda have been added. Use a wad of No. 2 or No. 3 steel wool for the scrubbing, then wash up well with clean water, using a sponge for the purpose.
¶ Oxalic Acid Bleach. Oxalic acid can be secured from any drug store and from paint store stocks in dry crystal form. Usually a saturated solution is made by dissolving as much of the acid crystals in a gallon of water as the water will take up. Hot water is best and the solution is more effective when put on to the surface to be bleached while it is very hot. Use an old flat wall brush or calcimine brush to apply the solution and let it dry on the surface. For bleaching weather stains and also dark sap streaks in wood 8 ounces of oxalic acid in two quarts of water is about right. If the first application of bleach does not remove the dis-colorations or make the whole surface as light as you want it, apply the same solution hot a second time or repeat several times.
¶ When sap streaks or whole surfaces to be bleached are greasy, wipe them off by rubbing with denatured alcohol and let dry before the bleaching solution is put on.
¶ Chlorinated Soda Bleach. When dissolved in water chlorinated soda makes an effective bleach, especially if followed by a solution of peroxide of hydrogen. To make chlorinated soda proceed as follows:
10 ½ ounces sal soda, dissolved in 20 ounces of water.
5 ounces ordinary chloride of lime (household).
Mix well by stirring and allow the solution to settle.
Mix solutions A and B together and you should have a clear liquid bleach of a greenish color having a faint odor of chlorine and a strong alkaline taste.
¶ Peroxide of Hydrogen Bleach. This chemical is a positive acting bleach when freshly made. It is a little expensive when large quantities are needed for large areas of surface. For small stains on patches and spots it is entirely practical. Brush on and allow to dry. Wash up with clear water.
¶ Hydro-Sulphite of Soda Bleach. When used in a 10 per cent solution,10 ounces of this chemical to 90 ounces of water, it makes an excellent bleach. Brush on one or several coats to the wood to be bleached. Let each coat dry, however, before another is put on. Wash up with clear water.
¶ Chlorinated Lime Bleach. For bleaching walnut especially, as well as other woods, the ordinary household chloride of lime dissolved in water and brushed on to wood is excellent.
¶ Permanganate of Potash Bleach. This chemical dissolved in water and used of varying strengths makes a good bleach. The wood will have a purple hue when dry. Apply with a brush. When the above solution is dry put on a second wash made by dissolving hyposulphite of soda in water, a saturated solution. This is the solution used by photographers for a fixing bath. A 5 per cent solution of oxalic acid in water is also effective as a second wash over permanganate of potash.
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