Urushiol! In black rings!

I came upon this sawn down tree on the edge of a parking lot. I hope the person who cut this tree down was either careful or immune to poison ivy, because lots of urushiol oil got sprayed around as the chainsaw cut through the tree and through a set of thick poison ivy vines.

The sap of poison ivy (and poison oak and poison sumac) contains lots of urushiol oil, which turns dark black after after a few minutes expose to air.

These two vines were both about an inch across, and both had the typical mass of red root hairs that attach the vine to a tree or a wall.

In Japan the urushiol from a related tree is used to make a fine black lacquer, but if you are highly allergic even that fully dried lacquer can give you a rash.