iandol on mon 2 oct 00
Hello again Janet,
I understand what you are saying. The temperature of the Arabian/Moorish =
lustre is much lower than that at which the glaze matures. I think we =
have to be careful to distinguish between reduction on the way to =
maturing a glaze when chemicals are in their raw state and reducing =
after a glaze has matured to a stable lead alumino silicate or soda boro =
silicate at a temperature at which it is just beginning to soften on =
reheating, round about 500Deg C. Robin Hopper also talks about lustre =
glazes where lustre flashing is done after quench cooling to about 650C, =
by reducing at constant temperature for up to an hour and a half. This =
can give brilliant metallic reduced copper red surfaces
I can see the advantage of making a reducing heat treatment on lead =
based enamels at a point at which they just become reactive and I have =
the facilities and materials to experiment with that. (Taught Enamelling =
at a school in Carlisle) This might be as low as 400C. The same thing =
applies to raku reductions as well. Much of the reaction takes place =
after the glaze is mature. But if you were to use one of the raw lead =
compounds such as lead carbonate of lead oxide and try to get that =
reduced raku effect before the glaze matured you would get chemical =
changes and lead metal forming. The difference between working at say =
cone 04 and cone 022 is considerable in chemical terms.
I achieve a very nice metallic silver yellow gold Arabian lustre on a =
stoneware glaze at 650C using Silver sulphide, which makes me suspect =
that the published chemistry, vis Hamer=92s Dictionary is somewhat awry. =
I did write to Prof Greenwood at Leeds University about this but he was =
unable to give me a definitive answer. Of course, Alan Caiger Smith is a =
past master at this technique.
Nice to hear from you again.
Best regards,=20
Ivor .
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