got it, that is ferric acetate! yeah, I have some oak that I could just turn purple/black without adding anything. I like the adding of the tannins first, that is a really good idea.
ferric nitrate turns oak purple/black due to tanins, too. But, I want to play with vinegaroon, now.
love the old names: aqua fortis, vinegaroon, etc. They are so much more expressive than chemical names.
thanks again,
kc