Crystalline Glazed Pottery
Crystals are not painted on the pots.
Just as water under the right conditions turns to snow,so a crystalline glaze under the precisely the right conditions develops crystals. There is however no guarantee that any crystals will be formed, or how many crystals there will be on any given piece.
The pots are first fired to 1000c called a bisque firing, the glaze is then applied, and the pot is fired again, this time to 1260c in an electric kiln.
Once the kiln reaches temperature, (1260c) the lid is lifted and the kiln is quickly cooled to 1000c. At this stage the glaze is in a molten state (similar to partially set jello)
The kiln temperature is held there for 4 to 6 hours. In this period two atoms come together and form a nucleus (seed), from which the crystals grow.
The glaze is comprised of approximately 25% zinc oxide, and 25% silica. They join in the firing process to form the natural mineral Willemite, also called Zinc Orthosilicate.
Colour in the glaze is created by oxides, such as cobalt, iron, copper, manganese, nickle and titanium. Combinations of these oxides create different colours.
Crystal growth is a very complicated and unpredictable process.
A pedestal the same diameter as the base of the pot is glued to the pot, this allows the glaze to flow off the pot and catch in the basin.
The glaze has no aluminum in it, making it very fluid at 1260c.
Once the pot is fired the pedestal is broken off leaving a rough surface that must be ground smooth.
Experimenting with post fire reduction. (That is firing the pots in a kiln atmosphere that is totally void of oxygen).
The hope is that the copper in the glaze will turn from green to copper red, either in the background or the crystals.
The first experiment, as you see by the pictures was dripping oil in the electric kiln.
The success was limited, and it did the kiln no good, it cost us a set of elements
The next idea was to try the Raku Kiln.
The results were still not what they were looking for.
Still a work in progress.
Below is a successful pot from the Electric Firing
........and one from the raku firing
Playing with Rare Earth Metals