Good afternoon, colleagues. This is a combination of wood species and the substance used to process the wood. A tree is an apple tree. The substance is ferrous sulfate,
https://en.wikipedia.org/wiki/Сульфат_ж% D0% B5% D0% BB% D0% B5% D0% B7% D0% B0 (II) When the apple tree is treated with an aqueous solution of this substance, the tree darkens. Then the tree needs to be processed with sandpaper. To achieve the desired effect of scuffs. When re-soaking this area of the tree with water, the tree darkens again.