I am an Endocrinologist, here's how it goes: green walnut peel stains your fingers brown. Someone way back noticed it looks like Lugol or betadine.
From here someone else thought IT IS iodine, - but it's not.....
It's an urban legend in Eastern Europe ("snake oil"). How can a 200 yo walnut tree find and pump yearly huge amounts of iodine in an iodine depleted area???
The brown stain is tannins used to process leather, and there is no iodine there.
If you ever find walnut tincture with iodine, someone added it (and it was not in the original walnul peel). As a specialist, I heard this from my Professor in the 90's and maked perfect sense.....
