Two new, small bowls from Garry oak. I ebonized the outside. This is done by treating them with a solution of iron dissolved in vinegar. The iron and the tannin in the wood react and turn black. I assume this is something like ink made from oak galls.
"Iron acetate solution prepared from steel wool and vinegar for ebonizing wood"
https://jwoodscience.springeropen.com/articles/10.1186/s10086-023-02079-0