Ron Roy on fri 25 mar 05
There is a basic misunderstanding in the following text - I'm surprised
nobody caught it.
Undisolved silica in a body is an anti craze - because it goes through the
quartz inversion during cooling - reducing the size of the ware and helping
to keep any glazes in compression.
Silica disolved in a body has a much lower expansion rate and would tend to
promote crazing.
Adding silica to a clay body helps to cure crazing because some of it
remains crystalline (quartz) and has a profound effect on promoting greater
body contraction during cooling.
RR
>There
>were crazing problems though due to the larger particle silica not being
>fully disolved in the body. I fire to cone 10 R and use a 12 hour firing
>from ambient temp to cone 10. Not enough heat work for the chunky
>stuff. I thought that these bodies would be good in a longer fire or a
>really protracted wood fire with a high end point like cone 12 plus.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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