Woodworker's Journal 2011-35-Winter, страница 35
Oxalic acid can remove iron stains from wood. Use proper precautions while mixing; flood it onto the wood; let dry; then use clean water to remove the residue. Chlorine bleach, applied top and bottom, will remove a variety of accidental stains but won't remove pigmented stains. Here, the swimming pool version... Clorox® on steroids — is shown on maple, walnut and mahogany. granules are sold at all different active bleach concentrations, so you'll have to read the label and do the math. Don gloves, flood the bleach on evenly and liberally, and let it dry. Remove any salt residue the next day by washing the surface with plenty of clean water, then wipe off the excess water and let the wood dry overnight. Oxalic Acid Sold as a dry crystalline powder, oxalic acid will remove blue-black iron stains that show up on oak and other high tannin woods, as well as some iron-based inks. Iron stains can come from hardware, cans or bits of steel wool that show up as tiny black dots in the oak pores. Widely sold as deck brightener, oxalic acid reverses the silver-gray of oxidized wood, but it won't change its original color, nor will it affect most wood stains or dyes. Oxalic acid is toxic and irritating to skin and mucous membranes in its dry form. Wear a dust mask and goggles while mixing it into water, and again when you sand the wood after the bleach has dried. Make a 6% solution by mixing about a tablespoon of it into one cup of warm water. Once it is mixed, it is fairly benign and won't smell much. Flood it onto the wood, let it dry, and wash off the salt residue the next day with clean water. Two-part Wood Bleach This is the one bleach that actually lightens the color of wood. Wood bleach will also knock out some, but not all, pigment stains but, curiously, won't affect most dyes. It is the most dangerous of the lot. Each component will burn your skin on contact; handle with care. Wood bleach is sold in two containers, usually labeled A and B — respectively, sodium hydroxide Oye) and hydrogen peroxide (not the 3% peroxide sold in pharmacies, but a wicked 35% concentration). Wet the wood thoroughly with the lye solution, followed quickly by the peroxide. When the two wet solutions come in contact with one another, they create a strong oxidizer that bleaches the color out of wood. It is important that the wood is still wet from solution A when the B is applied, so speed is of the essence. Pour each component into a glass, plastic or porcelain container for application. Wear gloves and goggles, and use synthetic brushes to apply the bleach. Some brands suggest mixing the two components together, then applying the solution. Again, speed is important, because the strongest action comes just after the two chemicals meet. Don't let the bleach contact metal, particularly steel wool, or it will quickly erupt into a Vesuvius of caustic foam. Let the wood dry overnight, and repeat the process if the wood isn't white enough. Once you're happy with the results, wash the surface with plenty of clean water to neutralize and remove the alkaline residue. Be careful when sanding: the bleaching doesn't penetrate deeply, and it's easy to sand through to the original wood color on the edges. & _ / Two-part bleach is the most dangerous. Use it with caution. Oil stain wINTER 2011 35 |
