Most glazes are applied to the piece either by brushing on or dipping into the glaze. The piece is then fired to a specific temperature which can range from 1600-2300 degrees Fahrenheit. Glazing is a very specific science that takes careful testing and formulating to master. Each type of clay body may require a different formula of glaze depending on the chemical composition of the clay and the desired outcome of the glaze.
Crystalline glazes are different from any other type of glaze. During the firing process crystals are 'seeded' and grown on the vessel. There is no special one ingredient that forms the crystal itself in the recipe of the glaze. Clay is generally added to a glaze so the glaze will stick to the piece, but this makes the glaze less transparent and interrupts the crystal formation. In crystalline glazes, since there is no clay in the glaze, it will flow downward when heated and there is nothing to make it stay where it is painted on.
To achieve the crystals on the vessel, the temperature and firing schedule are the most important factors. The kiln is heated at varying rates to the maturing temperature and then cooled at varying rates and held at key points to encourage the growth crystals. A computer is used to control the temperature inside the kiln and, once programmed, the computer can aide in making the necessary temperature changes to achieve the desired effect.
Since the glaze drips everywhere when fired, a special catch basin and pedestal must be custom-made to fit the bottom of each piece to catch the run-off so the pieces do not stick the shelves in the kiln or ruin them. Once the piece is fired, the catch basin is removed and the bottom of the piece is sanded down to be smooth and free of any rough edges that may have occurred from the catch basin. All of this is required to create just one vase, bowl, plate, etc. with the beautiful crystals.