Is a new grinding blank required every time a new piece of ground glass is made? I gave it a go this weekend but because I was anxious to try it out, I had a large piece of glass with a smaller (but still large, maybe 5x5 inches) piece of glass on top. I put some grit in between, added a few drops of water, and started going at it. The piece that I was using as a grinding blank (the two pieces of glass were equal in thickness), got ground before the piece that I intended to grind got ground. This may just be because of the size of the bottom piece though that I was trying to grind. I need to get my hands on a thick 3x3 piece or just cut a piece myself. Does the thickness of the grinding blank matter or is the only reason for its thickness is to make it easier to handle?