Why bleach?  Sometimes it’s all about what is currently the market trend.  Darker woods such as walnut, which are naturally dark in colour, may be bleached to a lighter colour, or even to white.  Light-coloured woods may be made lighter, or blonde. Or perhaps you are trying to subdue the rays, flecks and figure or control mineral streaks?

 Possible Reasons for Bleaching:

1. Dark Spots and Mineral Streaks
1. Maple often has dark spots

2. Iron Stains in Oak
1. Greenish or black stain often results after direct contact with iron
2. Caused due to a chemical reaction with the tannic acid occurring naturally in oak

3. Glue Stains
1. Oops!!

4. Blue Stain
1. Unsightly dark stains known as blue stain, sap stain or spalting can appear in the sapwood of some species
2. Spalting is due to the growth of fungi

5. Bleaching Walnut
1. Take care to avoid areas with a ‘purple’ cast as these may not bleach well turning a pink colour, or at best a pink streaking may occur
2. Some suggest applying a weak solution of a green stain to neutralize the ‘pink’

Bleaches work through a chemical reaction between the bleach solution and the colour in the wood.  The reactions differ from solution to solution – wood species to wood species.  Species do differ with the ease in which they can be bleached.  Always run a test piece prior to committing to an entire project. Thick pieces of wood cannot be bleached satisfactorily all the way through.  Work with the finished project; bleaching only the surface for the desired effect. 

If varnish, stain or other finishing product, including wax oil finishes, are present on the wood surface, they must be removed completely before the bleach solution is applied.  Wood bleaches might not bleach through the dyes or pigments used in stains.  Waxy materials may hinder the absorption of the bleach solution. Always give a final sanding before starting this process.

With small jobs or with very confined areas, such as mineral streaks, the bleaching solution can be applied with a cloth swab, brush or sponge.  Larger production jobs often require a spray gun.  Ensure the gun is equipped with a glass jar and the gun rinsed with water immediately after each use.

It is not a difficult process, however, selecting the proper solution does require some attention.  All of the chemicals used can be dangerous if used improperly.  Ensure adequate ventilation. Take care to protect yourself from direct contact and always read and follow the manufacturers’ instructions on the containers.  Wear gloves and goggles.  Keep water nearby and immediately rinse off any of the chemicals that touch your skin. 

The following recommendations are meant as a general guide to three bleaching solutions commonly available to woodworkers. 

1. Hydrogen Peroxide (30-35% strength)

• One of the most powerful, satisfactory solutions available
• Usually comes in two parts, commonly labelled A and B. “A” is usually sodium hydroxide and ‘B’ hydrogen peroxide; when the two are mixed, a strong oxidizing reaction takes place
• The chemical reaction on the wood, between the two chemicals, removes the colour of the wood; also may remove the natural lustre
• Used to lighten the natural colour; excellent in evening out colour variations between heartwood and sapwood
• This treatment does not work at all on some woods like ebony, and to varying effect on others if too much is put on; it can leave a greenish tinge on walnut
• Practice on a test piece!

2. Oxalic Acid

3. Chlorine

• Possibly the simplest method; readily available in a weak state as in laundry bleach
• Used to remove or lighten dye stains and food stains such as grape juice
• High concentration bleaches, such as those used for swimming pools, can be used for a more aggressive treatment 

After the Fact:  The final sanding will most likely remove any residual chemicals, but it is always preferable to rinse the wood with warm water upon completion of the bleaching job.  Allow enough time for the moisture and oxygen to leave the wood; suggested dry time 8 - 24 hours.  Failure to neutralize or remove chemical residue can result in hundreds of tiny bubbles and/or blistering in the final finish.  A final sanding will remove raised grain caused by the bleaching process.  Sand very lightly otherwise the thin layer of bleached wood may be cut through.

All references to bleaching solutions warn there are frustrations and certainly no guarantees to satisfaction.  Remember the kind of wood you have, the type of stain you want to remove, how the stain got there in the first place and how long the stain has been there all factors in to its effectiveness

What if?  Perhaps an opportunity to ignore these failures is offered here, and rather, an opportunity to allow your creative juices to flow is presented.  I read about a talented refinisher who carefully changed a small stain into a knot using an artist’s brush and some dark brown stain on a pine coffee table.  Upon completion, the ‘knot’ was unnoticeable and natural looking.  Clever!