Today I was using a DMT 220/325 plate to lap a Japanese 6000 grit stone that I have had for a while, but never used. After about ten minutes, I started to notice rough patches on the stone. Now the entire surface of the stone is covered in pits, and bits of stone came off when I rubbed it with my finger. Is the stone faulty, or did I do something wrong? Should I just keep going and hope that it gets better farther down? I have never had any problems lapping my Nortons, but I am new to all this and could use some advice.