Good to know and that is a much harder target to find! I think my mother in law has a bunch of wild black walnut growing on her land, I may have to harvest some next time they are in season. Also, I've tried coffee and tea and only tried painting it on like spirit dye. I have half a jar of instant coffee specifically for this still so I may need to get to soakin'! So basically anything that stains the sidewalk/driveway will do then.