Tuesday, September 23, 2014

eutectics


in which our plucky heroine digresses back to metal and glass for a moment...

There was some online discussion this week about using sterling instead of fine silver, for enameling. In both my own work and when teaching, I feel this is counter-productive, as the cost difference is minimal, compared to the effort needed to deal with the copper content in the sterling. What I have read is that you need to treat sterling in the same way you would treat copper, because the surface oxidises (turns dark) in the same way that copper does. If you depletion-gild the sterling then the outer surface would react more like fine silver. Using fine silver means that oxidation is not a problem because it (fire scale) doesn't happen on the surface. Fine silver and copper interact differently to different enamels, so sterling would have its own characteristic ways of reacting which you would have to learn. Sterling has a somewhat lower melting point than either pure silver or pure copper. In addition, if doing cloisonne, you would need to be careful about the fine silver wires touching the sterling surface. It is just so much simpler to use fine silver from the beginning, to avoid the hassles.

This is a piece I made back when I was beginning to learn enameling; we were taught to use copper as the base substrate. I took out of the kiln *just* as the eutectic action was in the middle of dissolving the wires... I had almost finished the enamel when this happened. I was able to salvage the work by creating a different pendant design, that worked with the changed enamel motif.

It was meant to say "enough is as good as a feast" and believe me bending those tiny little letters was not easy! The enamel is about 1 1/4 " across at the bottom edge. This is why I mostly never use copper as a substrate when doing cloisonne, the very slight added expense precludes a lot of heartbreak!
:::

melting point copper: 1,981°F (1083°C)
melting point fine silver: 1,763°F (961.8°C)
melting point sterling silver: 1,640°F (893°C)
melting point eutectic formation: 1,450°F (788°C)
:::

2 comments:

  1. I have used copper but there is nothing as beautiful to me as lovely clear glassy colors on fine silver! You must have felt so defeated-by-metals-and-heat when you saw your wires disappearing. . .

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  2. I remember how upset I was, but it has allowed me to keep my students from having potential discouragement at the very start of their enameling journey

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