Cracked Enamels

Studio artist Vicki Potter and I were talking about enamels yesterday. Vicki said:

After total success with my green flower necklace and another black and white necklace, I ran into some trouble with the yellows/oranges.  The enamel on all 3 of the flowers I did in those colors cracked.  So, I got out 3 more copper flowers and repeated the process all over again.  The same thing happened!  I’m pretty sure I did the exact same process with all of the pieces, as I was working in “batch mode”.  Any suggestions?

To which I replied:

That is COE (coefficient of expansion) at work. The enamel and the metal are expanding/contracting at slightly different rates as they heat and cool, and the glass, being the only thing that CAN break, does. I can’t say why one color worked and the other didn’t, but I’d guess that it’s either chemistry (different minerals used to color enamel = different rate of expansion), OR (more likely) that you used a heavier hand when sprinkling the yellow/orange enamel.

Are the flowers domed? A domed shape (even slightly domed) will resist the expanding and contracting movement.

Counter-enameling is probably the solution at this point, if you didn’t dome the metal. Next time you can work in a thicker gauge of metal. That will also prevent cracking of the enamels and warping of the metal.

Counter-enameling is putting a layer of enamel on the back of the piece to counteract the stresses caused by COE on the front of the piece. Almost all cracking in enamels is caused by COE problems. Some things disguise themselves as other types of problems, but they most often turn out to be COE issues. Taking enamels out of a hot kiln into a cold garage? Crack. That’s a COE problem. Enamel too thick? COE problems. No enamel on the back to counter the weight of the enamel on the front? COE problems. Warping caused by a rectangular shape? COE problems.

Oh, you can save your currently cracked flowers:

  • Enamel the back (I keep a container of contaminated and junky enamels to use as counter-enamel)
  • Fire upside down on a firing trivet
  • Clean up any marks left by the trivet with your alundum stone
  • Fire-polish

Remember to keep the torch off the front, if possible. It could discolor your enamels.

Let me know how it goes, Vicki, and thanks for letting me post this.

May 29, 2012