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updated fri 21 jul 00


Tom Buck on wed 19 jul 00

Joyce Lee asked about engobes and sparked this reply from me.
She asked me to send it to the list (with some minor changes):

Well, J: from my readings, etc., I'd say you're off the mark.
An engobe (a French word) is a type of slip that is adjusted to
shrink less than a slip because the engobe is meant for use mainly on
airdried ware (or biscuit) that already has gone through 5-9% shrinkage.
So, a typical decorating engobe has a reduced amount of claybody in its
makeup, as much as 50% non-clay components, and often one uses a
feldspathic material along with clay. To this mix one adds a few percent
or so of colourant.
There is confusion between slip and engobe because usually a
decorating slip is pure clay+colourant (I use my claybody+colourant) and
it is applied to leatherhard ware. Both shrink together. And if fired
without glaze to maturity sure it would be a "dry" finish, just like an
unglazed pot. But one normally bisques a slip-coated pot and then coats it
with glaze before doing the 2nd firing.
A decorating engobe would follow the same path but it is applied
to airdried ware most often, although some potters put it on biscuit (the
engobe for biscuit would have further reduced clay content).
There are also slip glazes: terracotta clays that become glazes at
c7/10. These would behave much like a clay slip (as above) so they would
be applied to leatherhard ware. If slip-glazes are handled properly, they
will give a glossy finish. The possible advantage with their use is
avoidance of the bisque-firing, ie, once-fired ware. The downside is that
slip-glazes usually are iron browns.

BFN. Peace. Tom.

Tom Buck ) tel: 905-389-2339 (westend Lake Ontario,
province of Ontario, Canada). mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada

Penny Hosler on thu 20 jul 00

Thank you thank you thank you. Finally, a straight answer. By
George, I think she's got it !
Penny in WA