Janet H Walker on mon 24 feb 97
You asked about copper reds via local reduction.
Sometime long past, I used a "local reduction copper red" glaze in
an electric kiln. It wasn't foolproof and often wasn't even red. I
don't have that recipe but recently started looking into the issue
again. I saw a suggestion somewhere about putting the silicon
carbide into a slip so I tried that.
Test:
mixed 100g of a white slip (recently posted by ?Vince P. I think)
added 1 g of 200mesh silicon carbide
Painted the slip onto greenware test saucers.
After drying, dipped the saucers into copper containing glazes,
one with 1% copper and one with 4% copper.
Fired to ^6.
Result:
Well, write this one up as one to avoid. The surfaces of both
were pebbly, with tiny tiny bubbles completely covering one of
them. No hint of redness anywhere. So, I don't know how many
of the circumstances were working against me, but in any case,
no copper red nowhere.
This issue has been studied and is reputed to be in several texts,
like Sanders (?) and Parmelee (?). Neither of which I've been able
to get hold of so I was playing around. Informing oneself ahead of
time with what has been tried already seems like a better starting
place.
Cheers,
Jan Walker
Martin Howard on tue 25 jul 00
In various postings I have read that one should use about .33% or .5% CuO
for Copper Red.
But how much SiC is necessary to bring about the local reduction in an
electric kiln?
What experience have ClayArters had of this process? Or is it just something
that appears in the various text books but with very little practice?
Has anyone used terra sigillata with silicon carbide, to emulate the black
terra sig of the Romans? Again, how much?
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
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