Tom Buck on fri 17 may 02
William H:
You didn't say bone dry. I assume leatherhard whenever anyone
says slip is being added to a clay vessel/pot.
I am trying to get everyone to agree on these definitions:
1) Clay slip / slip clay is a mix of clay and other materials such that
the clay components represent more than 50% by weight of the mixture,
usually well above 50%, and the slipclay will exhibit a drying shrinkage
similar to the claybody on which it is placed.
2) Engobe is a mix of minerals, chemicals, and clays such that the clays
are below 50%. (there is a sub-group, vitreous engobes, almost a glaze).
Most clayslips shrink like a claybody on drying, 5% approx., and
if this doesn't happen, the coating will fail.
Engobes will dry and fit the airdried claypot without cracking,
sluffing off. Hence, engobes must be formulated to achieve this. (hence,
swellable clays like bentonite and some kaolins should be avoided).
Several texts list engobes that have 40-45% clay, the rest
non-clay. and these will survive on an airdried surface.
Please come back to me and we can discuss your specific need in
more detail.
later. Peace. Tom B.
Tom Buck ) -- primary address. "alias"
or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
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