John and Dorothy Weber on mon 19 feb 01
I wondered if anyone can help on my formulation of my ash glaze. I runs =
and rivulets well, but in the runs, where it si thicker, it has a =
tendency to craze. I wanted to reformulate it by adjusting in small =
increments but wasn't sure which way to go. I fire to cone 10 in =
reduction using the following glaze:
Ball clay 16.7
Flint 12.5
Custer Feldspar 10.4
Whiting 10.4
Wood Ash - Oak 50
Bentonite 2
with analysis as follows:
Na2O 0.12 Al2O3 0.10 SiO2 0.91
K2O 0.13 P2O5 0.09
MgO 0.22 TiO2 0.01
CaO 0.54 Fe2O3 0.01
MnO 0.00
Thanks for your help. John Weber
Lili Krakowski on mon 19 feb 01
a lot of glazes will craze if applied too thickly or forming drops. The
usual craze cure is to add silica in small increments. A staight
line blend wold be good. As I do not have a book with limit formulas
with me. Check one of your books. figure out what the ultimate limit
for silica would be, use that as your end point for silica contents. Then
be sure to apply so that it DOES run. Good luck
Lili Krakowski
Craig Martell on mon 19 feb 01
John asked:
>I wondered if anyone can help on my formulation of my ash glaze. I runs
>and rivulets well, but in the runs, where it si thicker, it has a tendency
>to craze. I wanted to reformulate it by adjusting in small increments but
>wasn't sure which way to go. I fire to cone 10 in reduction using the
>following glaze:
Hi John:
As are most runny ash glazes, this one is a very hi flux glaze. The
alumina and silica are very low, according to your analysis. Another odd
thing is the level of Ca which is usually up in the .8 range for an ash
glaze that runs in rivulets. There are however, exceptions to everything.
Two things to try are: increasing the silica at probably 10% increments
since you are so low. Next you can add clay and silica keeping the Si/Al
ratio the same and do this in 10% increments as well.
The ash glazes that I use which have good fit, do not run. The silica is
at above 3.0 and the alumina is usually .28 and higher. You can achieve
better fit, but you may lose the runs. You won't know until you try.
regards, Craig Martell in Oregon
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