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I've been suffering with eruptions lately. I brought my schedule down to reasonable firing rates with plenty of bubble-squeeze time. Then I had another eruption of 2-1/2-inches right in the middle of a 12-inch disk. The eruption takes up the entire thickness of the glass, not just a layer.

The disk is a solid piece of 3mm glass, 12-inches in diameter. Then a layer of confetti glass. Then, topped with panels of cap glass.

I put the disk on Papyrus kiln paper. The paper is on a 12x13 ceramic plate which is on four 1/2-inch posts. I thought the paper would allow for some breathe-ability. Nope.

Here's my theory: I hate applying fresh glass-release on the ceramic plate, so if it isn't damaged, I just apply another coat. It got to be about 1/8-inch thick. (I'm a lazy newbie.) I've cleaned the kiln shelf. The coating easily cracked and flaked off the ceramic shelf in some places, but was tightly bonded for most of it. I think the loose-fitting glass-release had air trapped within it which would expand upwards into my glass platter during full fuse. I've been mis-diagnosing the problem and coming up with bad solutions.

I've cleaned the ceramic furniture. Since I have more shelf paper, should I use only that? Or should I do a couple thin layers of glass-release as well?

I think I know the answer to the question, but I'm more confident that I don't know anything.

Put a straight edge over your shelf. I suspect you will find a dimple under the place where the bubble blew up.

What's your schedule? Most likely, you're firing too fast from 1250 to your top temperature. And your top temperature is probably too high.

Another contributing factor may be that you may have less than two layers of glass with the lighter weight on top.

Thanks for the replies. These are good things to keep in mind.

I believe the issue was related to the build-up of glass release on the kiln shelf. Air below the built-up layers plus an uneven surface on the shelf combined to really screw me over. Learned my lesson. I'll be ordering a second shelf so I can be firing while I'm getting the other shelf ready.

The latest firing, just the shelf on posts with kiln paper, resulted in a nice and smooth platter.

The rest of the project was a weird result, but everything learned in stages, right?

You've got accessory glass placed between your two layers, right? That's a recipe called a Bubble Sandwich. Place your confetti on top instead.