Crystalline is a special effects glaze made primarily of particles of zinc oxide and silica. These two ingredients, along with others, are mixed with water and applied to the piece in a thick paste. Because the crystalline glaze is extremely runny at peak temperatures, a clay pedestal and glaze catch dish is made for each vase. As the glaze is flowing down the vase, the catch dish collects the excess glaze and prevents it from running onto and ruining the kiln shelves. While at peak temperature (around 2350 degrees F), a chemical reaction takes place between the zinc oxide and the silica forming seed crystals from which the crystal will eventually mature. After the chemical reaction is stimulated, the kiln is cooled 200 degrees below the peak temperature. The temperature is then held for 5 hours to allow the crystals to grow to the desired size. This is called the soak cycle. Once this cycle is completed, the kiln is turned off, and the crystal growth period is complete.
The crystalline glaze is white in color. Metallic pigments such as manganese dioxide, iron oxide, nickel oxide, cobalt carbonate, or copper carbonate as well as others, are added to create the wide color spectrum of the crystalline glaze. Once the kiln has cooled to room temperature, the vases and attached catch dishes are removed from the kiln. The next step in the process is removing the clay pedestals, which are still attached to the bottom of each vase. This is done by gently tapping the pedestal off using a mallet. The bottom of each vase must then be ground down in order to remove any excess glaze.
Take a closer look at crystalline here.