It hasn't when i used it that way.

I sure hope not because I'm using that on my headboards that would be a disaster...

Nope.

When I used it on my last project, I did have some slight scratching, but it's really not noticable.

I use iridized glass ALL of the time and don't have any problems scratching glass. There's hardly one of my mosaic that doesn't have iridized glass.

Are you all using sanded grout?

Haven't had any problems with it, but I do grout and clean more gently on them...don't know why, just seems the right way to do it.

Pat

nope, no problems here and I use sanded grout. I even tumble irridized glass.

I tumble it too, and don't have any problems.

Hazie

I use sanded grout and tumble my iridized glass without any problems. The only problem I have with iridized glass is the grinder chipping it. I have just ordered finer grit grinder bits so that should solve that problem.