Potassium dichromate was the go-to staining agent for wood for centuries. I'd bet a lot of our older cameras were stained with it.
Actually, it's not a stain, it's an oxidizer that darkens the natural tannins in the wood. The Dichromate is a bit toxic, so handle with care. But the results can be beautiful, it has a place in history, and as potassium dichromate has multiple uses in photography, you may have some around. Google it and you'll find many references:
https://www.woodworkersjournal.com/u...-stain-cherry/
https://www.lumberjocks.com/alindobra/blog/20036
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