A Brief History of Crystalline Glazes
Written by Adam Egenolf 
The first records of crystalline glazes being made are from the Orient, mainly China, many centuries ago. The Sung Dynasty (960-1279 AD) produced ancient Chinese oil spot glazes that contained small crystals in them, although growing the crystals was unplanned and unintentional. Later in 13th century China, during the Ming Dynasty, crystals were again accidentally formed. As far as written records show, there are not any other attempts to continue crystalline experimentation in the subsequent dynasties.
During the Art Nouveau movement, near the end of the 19th century, the style of a single glaze on a simple form began to have an appeal. Oriental glazes were being imitated and crystalline glazes, with their subtle color changes, fit into the natural and sensuous lines of Art Nouveau. Industrial ceramics and European potteries were making many stylistic and technological advances at that time, and the race for production and experimentation began. The crystalline glaze was seen as something new, and possibly profitable, if it could be refined and controlled. Although production and advancements were made by Europe into the first decade of the 20th century, nearly all crystalline work stopped at the beginning of World War One. The cost of making the crystalline production was too great, and with the low success percentage, the factories began to simplify their forms and use more consistent glazes.
The last and current big step in crystalline glazing is credited to the advancement of technology and the explosion of interest by the studio pottery movement. Studio potters have been using the new knowledge and technology for the last 50 years to experiment with crystalline glazes. The invention of the computerized kiln in the early 1980’s changed crystalline glazing forever. The precise control of temperature and the exact timing needed to grow a crystal in a glaze no longer has to be done with the artist standing by the kiln’s side. The human error in the timing of the firing process was all but eliminated. Chemistry and its advancements have also improved the precision and the range the potter can achieve. With the introduction of industrial frits and the purity of ingredients that can now be commonly purchased, the studio potter has increasing influence over many different variables that were previously uncontrollable.

The Crystalline Glazing Process
Written by Adam Egenolf  
Crystalline glazing is a process that involves a precise balance of clay, glaze, temperature, time, and form. If any one of these five parts of the process is not controlled in the intended way of the artist, the results will change. Because of this delicate balance, every variable possible must be addressed to give the best opportunity to make a successful crystalline glazed piece.
A crystalline glazed work of art starts with choosing the correct clay body for the desired results. The clay body that provides the most brilliant results is porcelain. Compared to other clay bodies, porcelain has the least amount of impurities, which yields a smooth, white, and blemish-free canvas to apply the glazes. The second step to create a successful crystalline piece is formulating a crystalline glaze recipe with the correct ingredients. Crystalline glazes contain three basic ingredients necessary for crystal growth: zinc oxide, silica (or ground quartz) and a frit which is fused glass that is ground to a fine powder. These three ingredients are mixed with water to form a thick glaze which is then applied to the pot. Various metallic oxides such as copper or cobalt oxide, iron, manganese or nickel oxide are added alone or in combination to give colors ranging from white to blue, green, gold, purple, orange, etc. Once the glaze has been applied to the piece it is then fired in the kiln to 2300 degrees. Once this temperature is reached the kiln is cooled quickly to suspend the runny glaze on the piece. The kiln must be maintained at this lower temperature for several hours to allow the crystals to grow. Since the glaze runs down the side of the piece it is important that every piece gets its own glaze catcher that it sits upon. This is to ensure that the glaze doesn’t ruin the kiln self that it is placed on. Every glaze catcher has to be then removed and the piece has to be ground flat with a diamond plated grinding disk. The crystalline process contains so many variables that consistent or predictable results are almost impossible to obtain.