Lisa P Skeen on sat 14 mar 98
Just recovering from workshop overload! First Mel's workshop in Pawley's
Island, then Byron's workshop at UNCG.
I got 3 of Byron's bowls, and have a question about one. The bowl in
question is salt fired white stoneware. The inside has a sort of green
hare's fur glaze, and the outside was left for the salt to cover. some reason, it has never dawned on me that the salt forms its own glaze;
I thought there were special glazes you used with salt for that orange
peel effect. DUH!>
So anyway, the question is this: The green glaze did not run or drip
down the outside, but some of that salt glaze is pale green. Does salt
steal the color from nearby glazes, or how does this color come about?
Lisa Skeen, Living Tree Pottery and Soaps
http://www.uncg.edu/~lpskeen
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Tom Buck on mon 16 mar 98
Lisa: If you can find Cardew's book Pioneer Pottery, and read his chpater
on glazes, you will be well rewarded with some insights into glazes.
Firstly, salt, ie NaCl, changes to Na2O in the intense heat of a
kiln at top temperature. This change tends to occur where heat can readily
be transferred to the salt fume (tiny particles), and this best occurs on
the surfaces of pots in the kiln. Na2O is a very powerful flux and will
convert alumino-silicates in the claybody to soda-based glasses. Because
claybodies are NOT microscopically uniform but full of irregularities
(chemically speaking), one gets the oilspot effect. And because clays
contain impurities, especially iron compounds, the iron will dissolve in
the soda glass and change its colour, with greens and blues being common
(celadon and chun).
Last I heard no one was doing much salt firing in electric
kilns...damage to the elements is too severe. So, a salt firing may be
seen as a modified reduction firing, hence, one can achieve some of the
colours produced by a kiln in reduction.
Tom Buck ) tel:
905-389-2339 & snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
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