Official Luthiers Forum!

Been a long time since I've had a problem, but today I bent up some Aussie Blackwood and it turned a lovely shade of green. I know it will sand out eventually, but I recall there may be a solution that removes the stain. Oaxic acid or something maybe?

Oxalic acid will do the job. Over do it, blackwood will go a bronzey colour. Not unattractive, but maybe not what you want. Wash the oxalic off with dilute white vinegar, then water. Anything with a basic pH (i.e. alkaline) will turn it green or black again.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Are you saying it will go a bronze color if I overdo the acid?

Yes. There is more red to the colour, heading in a mahogany direction. It's not unattractive, but may not be what you had in mind. Check it out on an off-cut. Some blackwood starts out that colour anyway, but if it went green on you it probably started out more on the brown side.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

I oversize my sides to possibly remove stains , anomalie,s etc with a very small sharp scraper blade as found in a stanley number 80 scraper

Thanks folks!

Fortunately most of it is on the inside. I reflect on the irony of how I can go dozens and dozens of guitars problem free on the budget line, but as soon as it's a show glossy with a deadline, things go squirrelly...

This is its color, and the color I'd like for it to stay.

I think this is the stuff I'm after?

https://www.homedepot.ca/en/home/p.all- ... 39775.html

Turns out you can get it in crystal form at Shoppers Drug Mart! That store gets better and better:)

Many paint stores carry oxalic acid. It is poisonous so use a little bit of care ( don't put it near your coffee mug).

I get it in crystal form from the hardware store, just labeled Oxalic Acid. Use "rubber" gloves.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Thanks Trevor! What is the mix ratio, and are nitrile gloves "rubber" enough?

Anything that will keep it off your hands. Nitrile should be fine.


The directions on my stuff say 250gm per litre. However, I use it at much lower dilutions, probably more like a tablespoon per pint, or a teaspoon per jam jar. Test, test, test. You may have to treat the back too, to get a good colour match.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Thanks very much!