| Potters work in mainly 4 categories
-Raku : 800-1000C (1470-1832F)
-Earthenware : 1000-1100C (1832-2013F)
-Stoneware : 1200- 1300C (2193-2372F)
-Porcelain : 1260-1330C (2300-2430F)
I fire the crystalline glazed ware to approximately 1280C (cone 10-11).
| Crystal glazes are a relatively new phenomenon.
There are not many examples before the early 20th century. The
early examples were discovered by accident without an understanding
of what happened. The ceramic industry
Europe and in America started experimenting
with the glaze in the late 1800's but
that the glaze was not practical economically
because of several factors which were
and time consuming. It was not until
1980's, when electronics started making
programmable, automatic kilns possible,
crystal glazed ware started to become
common. Even today, however, most potters
do not want to deal with the difficulties
involved in producing these glazes.
Crystal glazes require an intricate long cooling schedule. They run off the pot and need special containers to collect the running glaze so that it does not ruin the kiln shelves. It is impossible to repeat something again. Each piece is unique. Contrary to some ideas, we do not put crystals in the glaze, although we do sometimes for effect. The crystals actually form in the glaze in a chemical reaction during cooling and grow from small nuclei created during the melting process when silica and zinc come together to form zinc-silicate. I fire the crystal glazed ware to approximately 2340 degrees F. and then hold the temperature in the kiln on cooling between 2000 F. and 1830 F. for approximately 3 to 5 hours depending on the glaze.
Each glaze composition, together with the firing schedule and glaze thickness, makes different forms and colors of crystals. I use cobalt oxide, nickel oxide, iron oxide, copper oxide, and manganese oxide for different colored crystals.