Hi Min, I stopped using kiln wash a while back. It seemed to only be good the first couple of firings and then would start flaking off. It was a kiln wash mix from my clay supplier. It seems easier to grind the shelves than to repaint the kiln wash, and now I can flip the shelves and I've been doing it for a number of years. I do think that when the shelves get nasty, they reek havok on all my pots, not just bmix and porcelain.