Jeffrey Crowe on mon 2 nov 98
An earlier post had asked some questions on the differences between the
two states of zinc. I was using a historical bristol type glaze
(mid-range temp.) and it was recommended that calcined zinc be used in
the recipe. The calcined state is going to improve the raw glaze body
fit. I remember that the raw state was a bit lumpy and calcining broke
up the lumps somewhat. (But it still wasn't like baby powder!) There
was a color change in the powder from white to light yellow. (nothing
to get alarmed about). If you have access to Rhodes' Clay and Glazes
for the Potter", he has some comments on zinc oxide in his section on
bristol glazes.
I dont think you need to make any great adjustments to the percentage
of zinc in the glaze recipe. If you want find out how much weight
you lose when it is calcined, you could weigh out a set amount of the
raw, calcine it and reweigh. I imagine that the pecentage difference
wouldn't be so great as to affect the fired results. You will have to
test both versions. This might be a more economical way to process your
raw zinc than to hammer mill it ,(in less you need to process tons at a
time).
Jeff Crowe
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