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I have over 900 firings in this kiln and lately the large pieces have developed a large bubble while doing a full fuse -- a schedule that has worked well for years. Could it be the coils, heat, what???? I'm anxious for suggestions. I can return it to the manufacturer for an overhaul if push comes to shove. Help!

shelf warped

Might be a shelf warp, but a friend of mine experienced the same issue and has replaced her kilnshelf twice without relief. Check your kilnwash carefully.

Interesting, never thought about the shelf or wash. I have two shelves but I haven't correlated whether it happens on a particular one. I have switched my brand of wash, that might be a factor. I'll try experimenting, just hate wasting the materials.

Hi Babs,

Take the glass piece with the bubble and lay it on a flat surface. Does the non bubbled part lie flat or does in lift on two corners or sides? If the glass is warped then the shelf may have warped during firing and the glass is recording the shape of the kiln shelf at elevated temperature. I had a similar problem and noticed that the glass itself was no longer flat after firing. I changed shelves and the problem stopped. I use the "rogue" shelf for tack fusing now.

Brad has a FAQ on the large bubbles... might be helpful.

Cheers,

Bob

Thanks. I'm on a mission to solve and will report back.