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Oxalic Acid in Furniture Restoration

wood finishing

by Alan Noel
Professional Wood Finisher



Oxalic acid is a very useful tool when it comes to furniture restoration, as well as restoring an outdoor deck made with pressure treated pine.

Oxalic acid crystals are used in the restoration shop as a tool to bleach out rust stains from woods that contain tannin. When woods that contain tannin come into contact with moisture and iron, such as old nails and screws, a chemical reaction occurs. This reaction causes the surrounding areas of wood to turn black. We've all seen this effect on tops that were nailed down or around steel hinges.

An oxalic acid mixture will do wonders for wood that has been stripped and has that dull, grey and lifeless look. You can use it to bring back the natural color of outdoor decking as well.

Here are TWELVE tips on how to mix and use this very useful tool:

  1. Although oxalic acid is a relatively mild acid, always wear gloves when handling.
  2. Use glass jars to mix the acid in. Start by filling the jar two thirds full with hot water.
  3. Add the crystals slowly, stirring as you go.
  4. Keep adding crystals while stirring until the crystals begin to gather on the bottom of the jar.
  5. Stop adding the crystals. You now have a saturated solution of oxalic acid that can be stored indefinitely. Just shake it up!
  6. Apply the acid with an old wash cloth or plastic spray bottle making sure to wet the surface completely.
  7. Do not bleach only the areas that are discolored. You have to bleach the the entire area like a chest top or a table top. Otherwise it would be very difficult for even an experienced finisher to blend the areas together.
  8. Let the treatment dry and then wet again with water to see the results. Another application may be necessary.
  9. Since this is an acid, it has to be neutralized before any finishing can take place.
  10. Flood the surface with clean water and baking soda to neutralize the acid two or three times and leave to dry at least overnight.
  11. When completely dry, sand a small area lightly with 220 paper. If the sanding dust takes your breath away, neutralize again repeating step 10.
  12. Never mix oxalic acid with any other bleaches or chemicals.



Visiting Atlanta? Attend one of Alan's upcoming highly informative Highland Woodworking wood finishing seminars:


Spray Finishing, November 19, 2011

French Polish Workshop, December 14, 2011

Finishing the Finish, December 21, 2011

Visit Highland Woodworking's Online
Wood Finishing Supplies Department




Alan can be reached directly via email c/o Alan Noel Furniture Refinishing at anoelfurniturere@bellsouth.net.


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