Tom Buck on thu 5 jan 06
Carole:
so everything is coming up blue and no crazing! how come? the
answer may be that your very slow firing allowed the glaze to suck up some
clay body components, extra silica, extra alumina, extra ????
body and glaze always do interact, how much interaction is largely
due to the rate of firing and glaze coat thickness... more time to reach
maturity, means more time for body/glaze interaction.
this effect is educational... it reveals that glaze calculation is
a guide, not an absolute. when I did glzcalc on your glaze I got a COE of
8 x 10-6, and that for sure meant crazing. when I massaged the recipe I
couldn't get the COE down to 6.9/7.1 unless I made the silica and alumina
so high the glaze wouldn't melt at C6 (or so Insight suggested) but the
slow firing achieved exactly the melt you needed so you got the fit
you wanted.
I suspect glaze coat thickness had an effect also, but very hard
to evaluate.
BTW, did you do glzcalc on the revised raspberry? what did you get?
til later. peace Tom.
Tom Buck ) -- primary address.
"alias" or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
Carole Fox on sat 7 jan 06
Tom-
Sorry to take so long getting back- computer problems!
The expansion for the rasp. base with floating blue colorants came to 73.93.
Most of the recipes were in the 70 range for expansion. The Xavier Blue was
really nice and had a COE of 68.07, but it did not break gold the way my
floating blue does. The nice thing about the Xavier Blue was that it did not
show drips and stayed put even when on very thick.
My kiln is cooling now with large batch samples of FB. I hope that all goes
well. Thank you so much for your help and I am resolving to learn how to use
glazemaster this year!
Carole Fox
Silver Fox Pottery
Elkton, MD
silverfoxpottery@comcast.net
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