Ceramic Design Group on sun 25 nov 01
There has been some recent discourse on the formation of mullite in low
temperature bodies, or lack of it, and the resulting chipping that can
occur, not to mention delayed moisture crazing as the ware is quite open,
unvitrified, and punky. THe range of useable fluxes at that temperature
range, primarily talc, just doesn't form a very useable eutectic. I have
seen and used bodies in this range with not only talc, F-4, Neph Sy, flint,
etc. The temperature range just is not sufficient for proper glass formation
(unless, see below)
We have done some extensive research and testing into low temperature
earthenware and terra cotta bodies(cone 06-04) and many years ago decided
that working within that temperature range is not satisfactory for domestic
tableware, or what some may call useable pottery. I have long understood
that perhaps all of the commercially available under-glazes and glazes are
quite workable at elevated temperatures. With the exception of of the
commercial dipping clear glazes, which IMHO, form really poor glasses at any
temperature! We re-worked out terra cotta and earthenware bodies to be
completely vitrified at cone 3-4 and have all the same workable properties
that their lower fired counterparts have. We have formulas for plastic
bodies as well as casting bodies We can produce beautiful majolica at cone
3-4 on terra cotta as well as white ware that can be completely vitrified
and useable. The glazes at this temperature are well developed glasses with
all the properties that one requires for useable tabletop ware. No chipping,
no delayed moisture crazing, etc.
The other part of low temperature equation that works is the addition of
1-2% frit 3124 into the body formula. This results in a very durable terra
cotta or white ware body with good glaze properties. The only problem is
that this does increase the costs of the body, and the body sits on that
very narrow edge of being vitrified, eg temperature range for bisque and
glaze and if there are inconsistencies in kiln temperature, the ware is
exceedingly difficult to glaze.
Jonathan
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Jonathan Kaplan
CERAMIC DESIGN GROUP
PO Box 775112
Steamboat Springs, CO 80577
(970) 879-9139
info@ceramicdesigngroup.net
www.ceramicdesigngroup.net
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