My first test was black walnut…maybe it will have tannin because there are nuts, like oaks (source of gall nuts). I used the leaves of the black walnut tree–I set aside the walnuts which are immature at this point and I know will give a dark brown/black.
I was most impressed with the black of the black walnut as tannin sample. (In the middle) It was a stronger black than the gall nut. For fun, I dipped a sample in both tannin and aluminum acetate. Wowser…check out the yellow. And, as another control, the right hand one is ferrous sulfate only. Just rust color.
Questions that I have out of this test…what is giving the yellow? It happens in the presence of aluminum acetate and seems to be the prevalent color of my backyard tests.