Tom Buck on mon 6 mar 00
Tom Wirt asks about when reducing conditions are appropriate in a
fossil-fueled (gas, wood, oil) kiln.
Most popular glaze achieved under reducing conditions is Copper
red, a glaze that has long interested me so I have read extensively
about what other potters have tried and achieved with reduction firings.
And then did my own tests, etc., with some success.
The definitive report/article on the behaviour of the noble metals
in a kiln undergoing reduction is still available at www.digitalfire.com
and/or the Clayart Archives. It was written by Dr Karl Platt, a specialist
in glass technology, and was posted two-plus years ago. He goes into
superb detail on the chemical/physical activity in a melting glaze on a
pot.
As Platt notes, the individual potter needs to get a "feel" for
his system (body/glaze mix/kiln/firing conditions). In a typical kiln
firing, there are too many unkowns to set absolute rules on when to begin
reducing conditions, how long to continue, when to stop, when to do an
oxidation polishing (if ever).
My view is that moderate reduction should start reasonably early,
at or below 900 degrees Celsius, and continue until approaching C10. But
each glaze/body combination will require some fine-tuning of the regimen.
As Platt says: The essential step is the "dissolving" of the copper
compound in the glaze melt, and the subsequent formation of crystals of
the colourant on cooling.
Perhaps local potter Dale Mark, if he has time, will comment on
his practices. He makes porcelain functional ware, fires it to C10 (plus
or minus a tad), and produces gorgeous to my eyes copper reds.
til later. 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
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