Poplar finish

[Pete Staehling]

First let me say that I like poplar and use it fairly frequently as tonewood on musical instruments. I really like the natural color especially once the green goes away and it browns up a little. Actually I don't mind the green that much, but I think it puts off customers. I have a recent project that is done in clear lacquer and I love the creamy colors.

So that leads to some questions. Can oxalic acid turn the green to brown and not bleach the wood? Any suggestions on how to do that? How deep does the color change go? Can I still do a good bit of sanding and not lose the color?

[Jim Becker]

The greenish heart wood is going to change to brown on it's own via oxidation regardless of what you do. It doesn't really take all that long with UV exposure. Oxalic acid is going to bleach the wood...by it's nature it's considered "wood bleach". :) I really don't know how far it will penetrate, however.

Poplar is pretty nice relative to finishing flexibility. You can leave it natural as you have done, but you can also color it to spoof other, more expensive close-grain woods such as cherry or even go the other direction if your poplar is knotty and make it look like pine with a little more durability.

[Patrick Chase]

Oxalic acid has "paradoxical effects" on poplar heartwood. While it is a wood bleach and will lighten most woods, in that specific case it accelerates the green heartwood's browning (which would happen eventually anyway as Jim says).

[Pete Staehling]

Oxalic acid is going to bleach the wood...by it's nature it's considered "wood bleach".
Yeah, I read conflicting comments about that. The popular woodworking site had an article that seemed to imply that would the green a nice brown and the pale parts a warmer color. It sounded promising and I may experiment with it. I also will try to see how much UV exposure it takes to change the color. UV does sound more promising if it doesn't take too long.
https://www.popularwoodworking.com/american-woodworker-blog/make-poplar-look-pretty
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[Jim Becker]

I honestly was unaware of that particular potential property with poplar and oxalic acid. I may need to try it...we have oxalic acid because it's used to fight varroa mites with our honeybees and I have plenty of poplar. :) In my copious free time, of course...which means I'm waiting for you to try it and say if it works or not. LOL

[Patrick Chase]

I honestly was unaware of that particular potential property with poplar and oxalic acid. I may need to try it...we have oxalic acid because it's used to fight varroa mites with our honeybees and I have plenty of poplar. :) In my copious free time, of course...which means I'm waiting for you to try it and say if it works or not. LOL

One thing to note is that most bleaches (including all Chlorine-based ones IIRC and hydrogen peroxide) are oxidizing agents, while Oxalic acid is a reducing agent.

I suspect that the green extractive in poplar heartwood may brown when reduced, so the fact that oxalic acid is a bleach would be less significant/relevant than its role as a reducer. Just guesswork on my part, though it could be fun to test with non-bleaching reducing agents.

[Pete Staehling]

I was going to give it a test, but didn't find my oxalic acid. I guess it wasn't brought along when we moved to Tallahassee. I'll have to buy some oxalic acid and give it a try.

On the bleaching vs reducing agents... I wonder if you are correct in your guess. Do you have any reducing agents in mind as likely candidates? Hydrogen peroxide maybe?

[Pete Staehling]

Oh, by the way... On a different note I have had good luck ebonizing poplar to a nice dark color. That isn't what I am looking for here, but it did look nice.

[Jim Becker]

Oh, by the way... On a different note I have had good luck ebonizing poplar to a nice dark color. That isn't what I am looking for here, but it did look nice.
What was the process you used? 'Just curious... :)

[Pete Staehling]

What was the process you used? 'Just curious... :)
0000 Steel wool left in white vinegar for a few days. Poplar is wetted with tea before applying steel wool vinegar solution. I just applied with a paper towel. I also think I did some where the tea was just put in the steel wool vinegar solution. Both worked well. I was able to do sanding without losing color, but also found I could vary the darkness with heavier sanding. It is a messy process and stains hands, benches, and other things if you aren't careful. Gloves are recommended.

I don't remember if the tea was really required for the poplar. Some woods need it and some don't. Oak for example doesn't.

[Pete Staehling]

I did a quick test with peroxide and sun. The peroxide didn't make very much difference in a quick test, but the sun was amazingly quick. I put the pieces out for two hours of morning sun and the green turned a nice brown. The peroxide piece did seem to be a more uniform color, but it was subtle enough that it may be inconsistencies in my test.

Given how quick the sun worked I may not bother to try oxalic acid.

Edit: After more inspection, I think the peroxide piece is a nicer brown.

[Jim Becker]

I don't remember if the tea was really required for the poplar. Some woods need it and some don't. Oak for example doesn't.
The tannins are natively higher in oak, so the tea can be skipped. If I'm not mistaken, tannic acid is part of the particular process you describe. I haven't done it, but plan on giving it a whirl for a potential project I have planned.