Modification Date: 2016-09-09 22:16:32
A silky zinc-fluxed matte used historically across North America
Cone 6 glazes do not melt well using traditional fluxes (e.g. feldspar, calcium carbonate), they need help. In the past it was common to employ zinc, but today almost all medium temperature glazes depend on boron (from frits or Gerstley Borate). Zinc presents a number of issues, especially with color development, but in a white matte it is a viable option.
We have tested this recipe successfully on some occasions and had issues with it on others (stoney rather than silky matte). We are testing different cooling curves and different feldspars to determine the nature of its sensitivity. The mechanism of its matteness appears to depend on the firing. At times it is a silky matte that does not cutlery mark. Others times the zinc does what zinc does: grows crystals. A mesh of surface micro-crystals. These create tiny angular protrusions that abrade metal, leaving a mark (and a surface that stains easily).
Of course, the high feldspar content means that has a higher thermal expansion. This might be OK on stonewares, but on porcelains, where it gives the best surface, it crazes.
In Bound Links
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By Tony Hansen+