Tom Buck on sat 3 jan 98
The copper lustres are the ones subject to change in bright
sunlight... energetic photons cause copper metal to change to the oxides,
first to the red oxide, then the black oxide. Meanwhile, if the glaze
surface is inadequate and open to the atmosphere, then airborne sulfur
compounds as well as moisture will penetrate to the copper layer and
darken the colour markedly.
For a detailed look at this problem, and potential fixes, see
Ceramic Review #159 (May/June 1996) or go to Tony Hansen's website
and find the article there (or d/l same).
After I tested the new glaze mixes, with reasonable results, I
placed the test pots outdoors all summer, and learned that copper
metal simply will not remain stable in bright sunlight no matter
what. But the other three revised lustres were stable.
Tom Buck ) tel: 905-389-2339 & snailmail: 373 East
43rd St. Hamilton ON L8T 3E1 Canada (westend Lake Ontario, province of