Crystalline glazing is not for the faint of heart. It is a difficult and vast process which can be altered by many factors. It takes many years of trials and tribulations to establish what is called a 'good' crystal glaze. Everything about crystalline work is intricate and expensive; from throwing porcelain clay, to forming suitable vessels, to glazing and to firing. Yet, it is also very rewarding.
There are different types of crystals. What I focus on is what is called zinc silicate crystals. A basic crystalline glaze is made up of three main parts: zinc, glass former and flux. Colourants are added to this basic formula to create beautiful hues of blue, green, warm browns, ivory, yellow, pink, reds and violets. The trick is to differentiate the background colour from the crystal colour as well as to create a balanced ratio between background and crystal growth. This is where it gets tricky. Temperature, glaze thickness, glaze ingredients and form all dictates this delicate ratio.
The basic rules to crystalline work is to choose forms that are simple, elegant and which are conducive to flow. Then, a glaze is applied very thickly on the top of the vessel, medium in the middle and thin on the bottom. A catcher is attached to the bottom of the pieces to catch the glaze flow for crystalline glaze is very fluid. After this, the piece is placed in the kiln and fired to anywhere from cone 6 to cone 12 or 13. I fire to cone 10, which is approximately 1300 Celsius.
However, once I reach top temperature, I do not shut off the kiln. I actually fire the kiln as it cools, holding the temperature steady for many hours so that crystals will 'grow'. Varying where this hold takes place and for how long the hold is determines the size and the shape of the crystals. Going up and down in temperature creates what is called halos around the crystal. After the firing, the pedestal is removed with a torch and/or tapping and the bottom is sanded smooth.
No two pieces are alike. They are truly one-of-a-kind.
There are different types of crystals. What I focus on is what is called zinc silicate crystals. A basic crystalline glaze is made up of three main parts: zinc, glass former and flux. Colourants are added to this basic formula to create beautiful hues of blue, green, warm browns, ivory, yellow, pink, reds and violets. The trick is to differentiate the background colour from the crystal colour as well as to create a balanced ratio between background and crystal growth. This is where it gets tricky. Temperature, glaze thickness, glaze ingredients and form all dictates this delicate ratio.
The basic rules to crystalline work is to choose forms that are simple, elegant and which are conducive to flow. Then, a glaze is applied very thickly on the top of the vessel, medium in the middle and thin on the bottom. A catcher is attached to the bottom of the pieces to catch the glaze flow for crystalline glaze is very fluid. After this, the piece is placed in the kiln and fired to anywhere from cone 6 to cone 12 or 13. I fire to cone 10, which is approximately 1300 Celsius.
However, once I reach top temperature, I do not shut off the kiln. I actually fire the kiln as it cools, holding the temperature steady for many hours so that crystals will 'grow'. Varying where this hold takes place and for how long the hold is determines the size and the shape of the crystals. Going up and down in temperature creates what is called halos around the crystal. After the firing, the pedestal is removed with a torch and/or tapping and the bottom is sanded smooth.
No two pieces are alike. They are truly one-of-a-kind.