Hi - I was cleaning the bathtub w/bleach & forgot to drain it. It sat overnight with the bleach solution. The next morning there was a black ring right at the edge of the drain. It seems like something that seeps out from under the edge of the drain.. I can't get rid of it now, a little comes off at a time, but I can't seem to wipe it all off. Does anyone know what this substance is? Mainly I want to make sure it is not lead because it is the kids bathtub.
Thanks!:)

Bleach is powerful stuff. It may have degraded the gasket under the drain and carbon black is filtering out. This could also cause a leak. Tom can better explain how to take it apart and replace the gasket than I can.

"Bleach is powerful stuff. It may have degraded the gasket under the drain and carbon black is filtering out."

This is doubtful since the gasket is under the drain and not under the drain lip. We use plumbers putty to seal the lip of the drain. However It's possible that a handi-man missed the boat and installed the drain with the gasket under the drains lip. The one thing I can assure you is that it's not lead. Porcelain's a very porous material and the black will have t6o be leached out the same way it got in. Assuming Labs correct and it comes from the gasket you're going to soak the black ring with pads of paper towels soaked in more bleach and then try Comet and see it it can be scrubed out.
Good luck, Tom