Oxalic Acid and Iron Stains

The best use of oxalic acid is in countering iron stains caused by metal contact with natural wood tannins. June 17, 2010

I'm doing a project with 1/4 sawn sapele (ribbon stripe) and I have two stains right where I can't cut them out. This job is just going to get an oil finish, so they can't be stained out of sight. I run across these stains often on the thicker material and can often plane them out. This, however, is 4/4 and I'm at the 13/16" that I need. I've heard something about oxalic acid, but have no experience with it. Any ideas?

Forum Responses
(Finishing Forum)
From contributor R:
I don't know how big this piece is, but can you rout in a dutchman with the grain? Sapele has a strong grain pattern that will hide a dutchman easily...

From contributor C:
Oxalic acid is a mild bleach. Its main purpose is to act as a chelating agent to solve iron containing metal (ferrous metals) contamination that has resulted from the tannin in the wood contacting these metals. So unless it is this type of stain, it will do little good.

If you know what type of stains they are, post that info. If not, then all that can be done is guess work. If it is a fungal or bacterial growth, you may or may not be able to rid yourself of it.

Can you not buy another piece and plane it down? It seems it would be the quickest answer to your problem, rather than spending time and money trying to do something with no sure outcome.

From the original questioner:

Thanks. Routing the dutchman won't be possible in this application. I believe the stains come from the sticking process used when the material is kilned. I asked the wood purveyors that I deal with and they told me that the sticking setups are made of steel. So there you go. I usually can get the marks out, but I cheated this time. Generally I use 5/4" for my panels, but I am unable to get any in time for this job (lot of snow = no deliveries), so I'm using the 4/4" stock that I have here. I can get the acid right around the corner, so I'll try that today. If it doesn't work, I'll have to steal some material that I have set aside.