Wild Crafted Origin: United States. Description: The powdered hulls of black walnuts, which have a high tannin content, are made into tinctures and topical preparations. Because the hulls are also high in iodine, the powdered form is used as a supplement in regions where sea vegetables are in short supply. Ground black walnut hulls are used to produce a natural rinse to darken hair. The powdered hulls are also added to scrubs and powders for color.