Hydrogen Peroxide Bleach
One of the most powerful, satisfactory, and widely used bleaches in recent
years is based on a strong solution of hydrogen peroxide (30- or 35-percentstrength). The wood is first coated evenly with a solution of sodium hydroxide
(caustic soda, or ordinary lye) containing 4 pounds of the solid per ten gallons
of solution. After this has dried for about 30 minutes, an even coat of
the hydrogen peroxide is applied. The sodium hydroxide applied as the first
coat renders the hydrogen peroxide unstable, whereupon it decomposes and
liberates a large amount of oxygen in a chemically active condition, which
does the bleaching. The liquid on the surface should be allowed sufficient
time to dry, during which time the bleaching occurs; then the wood should
be rinsed thoroughly with cold water. To neutralize any remaining traces
of sodium hydroxide, the surface should then be washed or sprayed with a
solution containing I pound of acetic acid (or 1 pound of oxalic acid) per
10 gallons of water, allowed to staiid for 15 minutes, then rinsed thoroughly
with water and allowed to dry. After the wood is sanded lightly to remove
raised grain, the new finish may be applied. Several manufacturers and
dealers in hydrogen peroxide of 30- or 35-percent strength are listed in the
appendix.
Some furniture factories are reported to be using a process that eliminates
the sodium hydroxide solution. The wood is wet thoroughly with hydrogen
peroxide, then immediately moved to a room or tunnel where it is exposed to
ammonia fumes, either from ordinary aqueous ammonia solution or as dry
ammonia gas from cylinders. The advantages of this method are said to be
speed, economy, and the absence of nonvolatile alkali that must be removed
later from the wood by thorough washing by water. One writer states that tests
have shown that the ammonia method does not produce as white a bleach as
the older method does.
Prepared Bleaches
Perhaps the simplest method of obtaining a reliable bleach and becoming
familiar with the correct method of using it, is to purchase a prepared bleach.
Such bleaches often come in the form of two solutions, which may be mixed
immediately prior to application or used successively. If one application
does not give sufficient bleaching, several applications of the second solution
or of the mixture can be made. Several manufacturers are able to furnish
such bleaches, together with instructions for their use. Manufacturers of
prepared bleaches are listed in the appendix.
Oxalic Acid
Oxalic acid is frequently recommended and used where a comparatively mild
bleaching action will suffice. Recommendations as to its concentration vary
from 4 to 32 avoirdupois ounces of the crystalline or powdered oxalic acid