John Hesselberth on fri 20 may 05
Hi Everyone,
A few weeks ago I asked people to tell us how well (or not) the MC6G
glazes were fitting the clay bodies they were using. I now have data
on 42 clay bodies and thought you might be interested in the results to
date (by the way I would like to have more data so please send it you
me off-list if you are willing.)
There were no problems reported--either crazing or
shivering/dunting--with 35 of those clay bodies. Crazing was reported
on a couple of our glazes (Raspberry, Glossy Base #1 and/or Glossy
Clear Liner) for 2 bodies. Dunting was reported for a number of our
glazes on 5 clay bodies.
Dunting, of course, is the more serious defect. 4 of the 5 bodies were
from Standard Ceramic (112, 225, 181, and 245). The other was an A.R.T.
body (#103). To be fair to Standard, a number of their bodies were
reported to be fine with our glazes (306, 153, 200, 553, 563 were the
bodies reported to us so far. We also saw no problems with 365 in the
limited testing we did with it.)
When people have reported crazing to us (before we were keeping track
of specific clay bodies involved), we have been providing them with a
lower expansion version of the glaze in question and that seems to have
resolved the problem most of the time. We are certainly willing to help
anyone who runs into crazing problems.
We treat dunting problems a little differently. We have learned that at
least some of the dunting occurrences have been on bodies that contain
cristobalite. Ron's dilatometer helps us see that. Since we see no
value in having any measurable cristobalite in a cone 6 body--and some
good reasons not to--we usually recommend a body change if they want to
use our glazes. If they want to stay with that body we recommend they
use the body manufacturer's glazes which have presumably been
formulated to fit.
So far, we are pleased that our glazes are fitting such a high
percentage of the bodies our there, but we would like more data. Please
feel free to send it to me off-list at:
john@frogpondpottery.com
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
John Britt on sat 21 may 05
John,
You wrote:
"When people have reported crazing to us (before we were keeping track
of specific clay bodies involved), we have been providing them with a
lower expansion version of the glaze in question and that seems to have
resolved the problem most of the time. We are certainly willing to help
anyone who runs into crazing problems."
It might be very interesting to everyone on clayart to see how you
adjusted the original recipe to not craze on other bodies. What was the
recipe before and after?
Thanks,
President of the Glaze Recipe - Free Trade Association
John Britt
www.johnbrittpottery.com
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