Hairline cracks in enamel

25 september 2014 // Door webmaster //
28-01-2005
Hairline cracks in enamel.
29-01-2005
  1. Cracks are due to differences in the coefficients of expansion of metal and enamel. During firing and cooling down this gives rise to stresses which are usually absorbed by counter-enamel. Hairline cracks occur most often with transparent enamel.
  2. Hairlines are often due to uneven thickness of the enamel, applying it in too thick a coat, cooling the piece too rapidly, or not annealing the metal when it has been hand formed. Stress between metal and enamel may also arise from pressing too hard locally when stoning a piece after firing.
  3. The enamel is unsuitable for the metal to which it was applied because the coefficients of expansion differ too much.
  4. The enamel has been grossly overheated.
  5. When firing with the open torch large temperature gradients may arise in the enamel piece. This may give rise to cracks in the enamel, or to enamel chipping off.

Remedy: re-fire as soon as possible, before dirt accumulates in the cracks or the copper starts oxidizing. With transparant enamels the crack may become more noticeable due to oxides forming. In such a case remove the enamel from the crack, sand carefully, fill again with enamel and fire it.
In general: apply the enamel as evenly as possible.

See also:
Which metals are suitable for enamelling?
How to handle cracks in the enamel that reappear with each firing?

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