STOP!!! Are you steam cleaning your copings after you sandblast? If yes, DO NOT, just throw them in some distilled water and ultrasonic for 5 mins instead of steam cleaning after you sandblast. I know, it sounds silly, but try it...the problem is that the heating elements in the steamers are coated with a teflon material (which is great, makes them last a very long time) however, it contaminates the steam. This little bit of tidbit of info cost me over 25K and almost my sanity to figure out. Was getting bubbles (usually during glaze cycle),always coming from metal, changed crucibles, gasses, oxygen, different alloys, you name it....then Ernie from Ivoclar said they just threw all their steamers out the door, they found the same problem. Hope this helps and if not, maybe someone else.