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Understanding and Using Wood
Bleaches
Just as you can put color into wood with stain you can remove it
from the wood with bleach. Woodworkers often use wood bleaches to
lighten the natural color of woods or to even out color differences
between heart and sapwood. Bleaches can also be used to remove black
water stains, iron stains, and to lighten pigments and stains.
The bleaches work through a chemical reaction between the bleach
and the color in the wood. These reactions differ from bleach to
bleach and, as we will discuss later, the correct bleach will depend
on the situation. The bleaches don't actually remove the color from
the wood. They react with the chemical substances to convert them to a
substance that is colorless.
Bleaching wood is not difficult. Selecting the proper
bleach can require some attention. All of the chemicals used to bleach
wood can be dangerous if used improperly so care should be taken to
protect you from contact with their chemicals. Wear gloves and goggles
and read the direction on the container carefully. Two part bleaches
contain hydrogen peroxide, which will burn your skin. Keep water
nearby and immediately rinse off any of the bleach that touches your
skin.
These bleaches only work on bare wood so be sure to remove any
finishes before attempting to bleach the wood There are three primary
bleaches used by woodworkers today.
Two-Part bleaches are a combination of sodium hydroxide and
hydrogen peroxide. These bleaches are used to lighten the natural
color of the wood. They are sold in separate containers because they
chemically neutralize each other when mixed. When the chemicals are
mixed on the wood itself the reaction removes the color from the wood.
They can tend to remove the luster from wood as well so care should be
taken to test the results on a piece of scrap wood. Two part bleaches
remove the natural color of the wood and bleach it to an off-white
color. This type of bleach is also en excellent choice when you need
to even out the color variations between heartwood and sapwood before
applying a stain. The sodium hydroxide in two-part bleaches can burn
your skin so care should be taken to protect your skin and eyes.
Chlorine Bleach can be used to remove dye stain from wood in
much the same way that it removes color from clothing. Household
bleaches such as Chlorox can be used but they tend to be weak and
require multiple treatments. The shock treatments used for swimming
pools contain a higher concentration of chlorine bleach and can be
used for a more-aggressive bleaching treatment. Chlorine bleaches can
also be used to remove some food stains such as grape juice.
Oxalic Acid is an excellent choice for removing iron stains
and black water rings from old furniture. It is sold in a dry crystal
form and is available at most hardware stores. You will often see
oxalic acid labeled as "Wood Bleach" so check the label to
make sure you are getting the right product. It can also be used to
remove some inks and pigmented stains. Oxalic acid is also often found
in deck cleaners because it works well with old weathered wood.
Neutralizing Bleached after Use
After the bleaches have completed
their jobs they should be neutralized with water and then followed up
with a water/baking soda mix. Two-part bleaches can be neutralized
with a 1-part vinegar to 2-parts water bath.
This article is presented as a general guide to bleaches commonly
available to woodworkers. Before using bleach, you should read and
follow the manufacturers directions closely. Always test the results
on a scrap piece of wood or a part that is out of view in the case of
furniture restoration.
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