Homestead Finishing Products

General Finishing Forum - Neutralizing Oxalic Acid

Don Stephan - Sun Jun 27, 2010 4:26 pm
Post subject: Neutralizing Oxalic Acid
Instructions for using oxalic acid to remove black water stains on cherry include:
- wet the wood with distilled water
- while the wood wet, wipe with saturated solution of oxalic acid in water
- after overnight drying, wipe twice with distilled water, and finally
- wipe with baking soda solution to neutralize any remaining oxalic acid.

Everything worked well until the baking soda wipe, which made new black stains.

A new round of oxalic acid removed the new stains. Experimented today with the components to learn more. Using same plastic mixing tub, same new well rinsed sponge, and distilled water.

Wiping new distilled water on (new) test piece of cherry produced no stains. Wiping new saturated oxalic acid solution produced no stains. Wiping saturated solution of Arm & Hammer Pure Baking Soda produced significant, uniform black stains.

The intended finish will be one or two coats of danish oil. Any thoughts on the baking soda problem? I'd like to neutralize the oxalic acid with something. Seems like weak baking soda solution might still produce some color shift in the cherry.

mdclor - Sun Jun 27, 2010 7:30 pm
Post subject:
Lye and ammonia are also basic. You could try either one or both (separately) to see if they also produce the black stains. Be careful with both, but the lye is the worse of the two. As always, test on scrap first.
Don Stephan - Mon Jun 28, 2010 11:15 pm
Post subject:
After allowing time for thorough drying, and then examining the results in better light, the concentrated solution of baking soda did NOT cause black stains on the cherry. Perhaps in my initial work the mixing container for the baking soda had iron contamination.
Interestingly, the concentrated baking soda solution DID turn the cherry a strong dark red. The color may be similar to that produced by lye, if soneome wants to experiment and compare. I wouldn't risk using lye personally.
R Boardman - Tue Jun 29, 2010 11:46 am
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Cherry turns dark when in contact with iron or other metals....metals typically found in tap water. Try a weak solution of baking soda mixed with distilled water...that should solve the problem.
Wood Finisher - Sun Jul 04, 2010 10:53 am
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Don -
I wonder if you can get away with a little vinegar to neutralize the acid -

R Boardman - Sun Jul 04, 2010 5:29 pm
Post subject:

Vinegar is's chemical name is acetic acid
Wood Finisher - Mon Jul 05, 2010 11:08 am
Post subject:
Happy 4th - R Boardman
Thanks for the info -

To: Don -
My schedule for treating the surface following oxalic acid is to just wash off the residue very well with water.
I never had a finishing problem from Oxalic acid nor have I ever needed to use the baking soda .

Don Stephan - Mon Jul 05, 2010 7:37 pm
Post subject:
I've repeated the oxalic acid and baking soda three times with the same result. The last concentration of baking soda was 7 grams (1/4 oz) in 4 oz (1/4 pint) and still had blotchy areas. At first I thought there might be something unique about the veneer supplied for Shaker oval boxes, but the same happened with a piece of qs cherry lumber. Distilled water throughout, same plastic mixing tub. the only think I overlooked was I used one new plastic picnic spoon throughout for the oxalic acid and a different new one throughout for the baking soda.
These were practice boxes anyway. One I just rinsed well after the oxalic acid dried and applied Danish oil - seems okay. The other two I'll apply the Danish oil over the blotchiness and see if it darkens uniformly.
Interestingly, a saturated baking soda solution turned the sample board uniformly dark. Equally interesting, when I re-did the sample boxes a new application of fresh oxalic acid removed the blotchy baking soda effect.
Thanks all.
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