Marks on tile from Regrout Job

Well I finished my re-grouting job. Since my Fein Multimaster was stolen, I bought a new Porter Cable oscillating tool and 2 diamond bits (one came with it) to do the job. Everything was fine until about 2/3 of the way through, when my brand new tool starting making a horrible noise, and the blade was vibrating terribly. Upon inspection I found that the quick change mechanism that holds the blade in place was defective, and was no longer able to hold the blade in place properly. On top of that, I couldn't even get the blade out of the unit! I thought Porter Cable was supposed to be decent quality, but... I took it back today and got a refund. Now I'm shopping for a new unit, and input would be appreciated.

Anyway, that's not the reason for the thread. While removing the tile, the tool slipped in a few places and while it didn't cut the tile, it left a few black marks on the white ceramic tile that I cant get off. I've tried everything I had: grout cleaners, tile cleaners, mild acid cleaner, barkeepers friend (which normally take black marks off of bathtubs when nothing else works), acetone, lacquer thinner, you name it. It's actually a very slight scratch that is black. Any ideas from you pros on what might take it off? Bleach maybe? I have to go back next week to resurface that bathtub, and I told him I'd find something to use by then. HELP!!!

Barry

Can you feel it if you use your fingernail? Is it through the glaze? If it's just on the surface, it should come off. As indicated, toothpaste, being a mild abrasive, would probably work. Too abrasive, and you'll dull the glaze's finish, and maybe make it worse.