I've been researching extensivly, but can't get a defininate answer on this. I have an old kiln shelf I am ready to cut to fit my oven my question is that there is old glaze spots on one side that I could grind off, but would that be safe to use?  I've seen some posts that say there could be resididuel lead inside the shelf that could leach out and some that say that glaze is fired at 1400 degrees so there is no way a home oven maxing out at 550 could even soften it. I'll take any advice, the shelf was free from an old shed at a relitives house. One side is untouched if that matters. thanks in advance-george