Dave Finkelnburg on tue 6 apr 04
Daniel,
You are absolutely right when you write, "....it appears that for really
> accurate calcs. you should recalc the SG for your glaze/slip for each
> recipe...."
I don't think that sort of accuracy is necessary, or worthwhile, in a
studio pottery setting. However, it does make sense to use an average dry
material density in the formula that is closer to the average of your glaze
ingredients than the density of clay casting slip, which is what Monsieur
Brongniart used, because he was slipcasting for the most part rather than
glazing.
For that reason, I use a density of 2.64 grams/ml, rather than the 2.5
he used. As many sources have observed, were one to use fritted lead
glazes, the density would be quite a bit higher and the difference would be
very significant. My change only causes a difference of about 4% in the dry
weight determined using the density of a glaze slurry. That's not a huge
difference, but the effort to determine that helped me understand the
formula and use it, hopefully, correctly.
Good glazing!
Dave Finkelnburg
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