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lowfire claybody

updated wed 1 feb 06


Tom Buck on tue 31 jan 06

Perhaps you have a copy of Michael Cardew's "Pioneer Pottery" --
should you be so fortunate, then please review the Chapter titled "Clay".
He gives you a picture of the different types of clay and where you'd
likely find them.
FYI, my bungalow sits on the Niagara Escarpment (a flat plateau
that, in part, keeps Lake Erie separate from Lake Ontario; hence the
existence of world-famous Niagara Falls). What is notable about the
Escarpment is the bedrock (an old lakeshore) of almost pure limestone, and
ontop of this limestone sits a few metres of "soil" ... including in many
places a metre of clay below the topsoil... the clay was deposited ontop
of the limetsone over geological ages due to the fact that much of the
Escarpment is a flood-plain.
A few years ago, while adding a new room, the backhoe dug down
approximately 2 metres, and brought up a lot (tonne?) of clay. I grabbed
up to 100 kilograms of this raw material and processed it as Cardew
suggests, and recovered up to 60 kg of fine-particled clay. It was light
tan in colour (elsewhere such clay likely had hues of blue, green and
Now came tests. I assumed it would be "earthenware" "terracotta"
so fired it to Cone 010 (raku) and Cone 06/04, and the pots survived
although somewhat high in porosity. Onto Cone 5/6, and the pots slumped
badly, At Cone 10, the clay was a natural glaze, quite a nice mid-brown.
If one visits the shores of Lake Ontario one often comes across
huge deposits of "slate" - this is a form of shale (aka fossilized clay).
One can readily expect therefore that any secondary (sedimentary) clay
deposits on (or below) the Escarpment will contain significant amounts of
compounds of Calcium, Magnesium, and often Iron, perhaps as much as 12
weight percent. These additions to Alumino-Silicate material (kaolin or
kalonite materials) account for its low fusibility.
I'd be surprised if Annapoorna was unable to find some useable
clay on a riverbank close her studio. When she does she can expect it to
be an "earthenware" reasonably plastic and serviceable to Cone 06/04.
and perhaps some kind Claybud would send her a copy of Pioneer
Pottery so she would see how to look for clay, process it, and make pots.
(Sorry, she can't have my copy right now).

be well. peace. Tom.

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