Coffee, tea, tobacco and black walnut hulls are all well known fabric dyes. Not sure how they would work on ivory. I have a wooden spoon that has taken on a yellow color after using it to stir my home made chicken noodle soup that contains a hefty amount of Turmeric. Nothing has stained that spoon in the 40+ yrs that I have used it until this. The color doesn't want to wipe off either.
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