Janet Kaiser on sat 21 aug 99
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Bloating is caused by development of gas pockets in a body after it has =
started
to vitrify and is pyroplastic. The causes can be anything from dirty clay to
poor preparation to sulfides to over-firing to pockets of water, etc. etc.
Firstly, can you categorically say that it is not due to bad mixing or =
wedging?
Yes? Then there are other options to question, try out, test and adapt, =
before
blaming the clay...
At least that is what I was taught. But then again, that was in the days =
when
potters had to work hard on the clay before they could start the =
=22creative=22 part
of the process. No just ripping open a plastic bag straight from the =
supplier,
followed by a bit of slap-and-tickle and straight to the wheel. What about
trying the simple addition of some opening material such as grog?
No change? Then what about reviewing the firing process? Care must be taken =
to
avoid vitrification during the biscuit firing. No sudden or local =
temperature
rise should take place, especially in bodies high in carbonates. Then what =
about
during the final firing? Cardew recommended maintaining oxidizing conditions=
to
1150 deg. Celsius in the stoneware firing and David Leach suggests an =
oxidised
soaking at 1000 deg. Celsius to burn out carbon. So the =22recommended=22 =
cone 10 is
too high? Why not try 9 instead? Once again, it is a combination of =
experience,
application and (dare I say it?) intuition.
I know I am sticking my neck out again =3Elopsided grin=3C
BUT, I do feel that a little too much dependence is put into what the
manufacturers must/have to list as a =22full description=22. Clay varies so =
much
from batch to batch, week to week and even bag to bag, so can never be
absolutely =22constant=22. The Masters did/do not depend on the supplier =
stating
cone this or that. They worked with very basic materials and methods to =
produce
their wares and I bet when they sourced a new clay, certainly did not rush =
into
producing whole kiln-loads without trying it out first.
Certainly a potter depends on a certain consistency of a batch of named clay
from a supplier, but on the other hand everyone is behoven to go through a
testing process before using any new material. Especially something as =
complex
as clay.
If, after all the variables have been tried and it can be fairly suspected =
that
there is something inherently =22wrong=22 with the clay, then it is fair =
enough to
start questioning the supplier. IMHO it is unfair to expect something as =
complex
as clay to be as =22constant=22 as something simple, such as salt. And I =
think most
experienced potters would agree?
Janet Kaiser awaiting her Kiwi cousin from Down Under to arrive for a =
visit, so
I can tie him to the PC until he sorts out the dire problems in person, =
instead
of e-mailing from afar and telling me what to do in unintelligible lingo.
The Chapel of Art, Criccieth LL52 0EA, GB-Wales
Home of The International Potters Path
WEBSITE: http://www.the-coa.org.uk
EMAIL: postbox=40the-coa.org.uk
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