David Malicky on sat 22 jul 00
i have a number of recipes that are nice except that they craze. i noticed A.R.T.
sells "amorphous silica" which is said to reduce crazing. does anyone know
how well it works? are there any drawbacks?
thanks,
dave
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David Malicky
Mechanical Engineering Department
Valparaiso University
David.Malicky@valpo.edu
http://diamond.gem.valpo.edu/~dmalicky/
219-464-5062
Craig Martell on sun 23 jul 00
Hello David:
I think that the word to focus on in the ART claim about crazing is:
"reduces". What you want to do is "eliminate" the situation.
The idea has been that ultra fine silica will bond more readily to the
clay/glaze interface thereby lessening the tendency for a glaze to craze.
The fine particle size requrires less heat to enter fusions. I tested some
silicas years ago to see how much the ultrafines would help. I used Imsil
A-25 mainly, which is about 400 mesh. It cured one glaze which was very
close to fitting the others still crazed. There really isn't a problem
using this stuff in glazes and most silicas for glazes are very fine. Not
good for claybodies though.
The most effective approach to crazing is to look at the coefficient of
expansion of the glaze and work with the seger formula to adjust the
calculated expansion. If you make your clay you can also adjust the body
if necessary. If you use commercially prepared clay, you can test several
others and see if you find one that promotes glaze fit.
later, Craig Martell in Oregon
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