The Crystals on my work are zinc, silica, frit 4110, rutile and titanium dioxide. Metallic oxides used are, Copper Cobalt, Nickel and Manganese
A Crystalline glaze is fired higher than the melting temperature of the glaze in order to liquefy the glaze completely (1280 to 1300 degrees Celsius).
I then reduce the kiln temperature to the range for crystal formation, (about 1100 degrees Celsius) and hold it there for between 2 to 4 hours depending on the size of the crystals I want to grow. The shape of the crystal is determined by both time and temperature.
Crystal glazes must be very fluid to enable the crystals to grow so each pot has to have its own saucer to catch this flowing glaze.Some of the glaze then runs off the pot during firing and each pot must be separated from its base by cutting and grinding with a diamond saw blade. This process leads to a high loss rate, particularly for the larger pots.
Crystalline glazes are not used in mass production because they are too unpredictable and time consuming.
Each pot will be different and each piece having its own unique arrangement of crystals. The aim is for the crystals to be well distributed and in harmony with the form of the pot.
Crystalline glazes are spectacular and for centuries have been widely regarded as the most challenging glaze technique a potter can endeavour to master.
Kees Staps
