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Enamel on hollow formed shapes - HELP


My student is hollow forming pods and soldering them together with extra hard solder, then enameling. Went fine last semester, but they are having an issue with the enamel cracking just out of the kiln. We made a small “housing” of firebricks so that they cool slower, but about every 3rd one cracks off. I am attaching a picture. Enameling is not my highest skill so other than clean metals, cooling slowly and thinnner layers I’m not sure what else to suggest.


If the back were open counter enameling would likely help. But with a closed hollow form I don’t know how you’d do it.
James Miller is the man to ask.


This sounds like a frustrating yet interesting issue, i hope to learn more along with you!

…I was wondering…

are the hollow forms annealed before enameling…

are all the enamels the same coefficient of expansion…

how many layers are you firing……thick?…thin?
colors layered…side by side

could you counter enamel the inside, then enamel the outside, and then cold connect the two enameled halves together…

…this link is interesting…re expansion and colors side by side…


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Your question brings up more questions. Have you counter enameled the formed metal? Is the back solid and closed? My first thought is the stress that’s going on with the soldered edge and no counterenamel being the cause of the cracking. When the enamel and metal cool - regardless of how slowly - the changes in the expansion/contraction of the metal that cause stress on the glass/enamel may be too much for the glass…consequently, the glass has to break to relieve the stess.


Is the metal being cleaned well enough?

Also, submerging the just fired pieces in a bucket of vermiculite chips I believe is what my cloisonné teacher suggested to slow cooling and prevent cracking

You can purchase Japanese annealing bubbles from that will help with cooling, and they are not as messy as vermiculite. I keep them in a cookie tin, and use them for lampwork that I cannot put straight into the kiln to help them cool more slowly. Cooling may not be the issue though - might be lack of counter enamel as has been suggested. I have never enameled on hollow forms, so not sure how to resolve that.


I’ve not got a lot of enameling experience, but I have had some success with solving the cracking problem by putting some vermiculite in a small crockpot (think they’re called Little Dippers) set on low. The crockpot keeps it warm enough to slow down the cooling sufficiently to prevent cracks. I wasn’t making hollow forms, but did do some pretty small pieces without cracking.