About Crystalline Glaze History and Technique

spiral Potters work in mainly 4 categories spiral

  -Raku : 800-1000C  (1470-1832F)

  -Earthenware : 1000-1100C  (1832-2013F)

  -Stoneware : 1200- 1300C  (2193-2372F)

  -Porcelain : 1260-1330C  (2300-2430F)

spiral I fire the crystalline glazed ware to approximately 1280C (cone 10-11).  
I use 4 different porcelain and stoneware clays that come from Alberta, Seattle, and California.   

2004, Bill Boyd
spiral 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 in Europe and in America started experimenting with the glaze in the late 1800's but decided that the glaze was not practical economically because of several factors which were difficult and time consuming. It was not until the 1980's, when electronics started making fully programmable, automatic kilns possible, that crystal glazed ware started to become more common. Even today, however, most potters do not want to deal with the difficulties involved in producing these glazes.

spiral 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.

Artist Statement

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