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engobes and slips

updated wed 26 jul 00


Tom Buck on mon 24 jul 00

A post today cites Hamer's dictonary to say Hamer regards a slip glaze as
one that has 50% or more clay in its makeup, not 100% clay as I stated.

Well, Mr Hamer uses a different definition for "slip glaze" than I
do.... not an uncommon occurrence between UK practice and North American
procedures. Our heritage in N. America is based on clays like Albany slip
that were used as-is in pioneer potteries to coat jugs, etc.
If I were writing the book I'd say "high-clay glazes" for what
Hamer describes and "slip glazes" for clay-only (+small amounts of
colourant if needed). Yet, since most earthenware clays (terracotta clays)
are high iron clays, they become glassy at high cones and yield a
mid-brown to dark brown hue, not something you'd want to add cobalt oxide
But yes, as cited in an earlier post, it would be worthwhile to
add 10% Zirconium Silicate to a natural clay like Albany slip and the
highly refractory Zirconium compound would likely make the surface
A final note: a "slip glaze" is a natural clay that will become a
glass at high cones; whereas a "clay slip", coloured or not, is used to
decorate wetware, and fires to a dry clay finish if uncoated.

BFN. Peace. Tom B.

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