[Timothy Terwilliker (OP)]

i was browsing youtube a few years ago and saw a video that showed a guy fermenting tea bags in white vinegar and the result was oxalic acid which he used as wood stain. Was this fake or did he just make something else? if so how would i make some at home?

[Bored chemist]

Oxalic acid bleaches wood...

[Kryptid]

Page 499 of this old chemistry book states that oxalic acid can be acquired by mixing sawdust with potassium hydroxide: https://babel.hathitrust.org/cgi/pt?id=uc2.ark:/13960/t3tt4gz1p;view=1up;seq=527

[Colin2B]

i was browsing youtube a few years ago and saw a video that showed a guy fermenting tea bags in white vinegar and the result was oxalic acid which he used as wood stain. Was this fake or did he just make something else? if so how would i make some at home?

I don’t think he was making oxalic acid, he was getting tanin from the tea bag. If you put iron eg wire wool in acidified tannin you get a black stain which you can use on wood.
You can extract oxalic acid from rhubarb leaves using calcium carbonate to create oxalate crystals, but as @Bored chemist says this is a wood bleach not a dye.

[pensador]

Oxalis removes rust.

Amusingly my misses likes to dye fabric, and was experimenting with rust on the fabric. She made some very pretty patterns which she then over dyed with some oxalis pes-caprae https://en.wikipedia.org/wiki/Oxalis_pes-caprae. The rust patterns she had on the fabric completely disappeared and she had a wonderful yellow fabric and no rust patterns anymore.

The lesson she learned was Oxalis Pes-caprae contains oxalic acid. 

[Bored chemist]

Page 499 of this old chemistry book states that oxalic acid can be acquired by mixing sawdust with potassium hydroxide: https://babel.hathitrust.org/cgi/pt?id=uc2.ark:/13960/t3tt4gz1p;view=1up;seq=527

That link didn't work for me.
How about this?
https://thesis.library.caltech.edu/487/1/Alcock_jr_1923.pdf

It's fair to say that molten caustic is not much nicer to work with than nitric acid, but it is easier to get and probably fumes less (though you should beware of the production of carbon monoxide).

[Timothy Terwilliker (OP)]

Thanks for the answers. I'm definitely going to try the sawdust method but i'm a bit confused as to how the oxalic acid is separated from the rest of the mixture.

[Colin2B]

Oxalis removes rust.

Amusingly my misses likes to dye fabric, and was experimenting with rust on the fabric. She made some very pretty patterns which she then over dyed with some oxalis pes-caprae https://en.wikipedia.org/wiki/Oxalis_pes-caprae. The rust patterns she had on the fabric completely disappeared and she had a wonderful yellow fabric and no rust patterns anymore.

The lesson she learned was Oxalis Pes-caprae contains oxalic acid. 

I often use oxalic acid to remove rust and stains on a boat, but there you can wash away the resulting ferric oxalate which is yellow/green. I assume this is what has stayed in the fabric, pity it wasn’t possible to fix the design first. Maybe one of our chemists has thoughts on how to do that.