Crystalline glazes

The first crystalline glazes are believed to have originated during the Song Dynasty (960 – 1279) in China. The Chinese iron-rich harp fur glazes contained small microcrystals. In Europe, the experimentation with glazes did not begin until porcelain clay, which can be fired at high temperatures, began to be used in France in the latter half of the 18th century. It was discovered that an excess of zinc oxide led to crystal formation – but the crystals were considered a mistake. With Art Nouveau’s interest in organic forms, ceramics affiliated with the Sèvres porcelain factory in France, Royal Copenhagen in Denmark and Meissen in Germany, among others, began experimenting with crystalline glazes. Modernism’s focus on undecorated surfaces led to a decrease in interest in the expressive crystal glazes, but since the 1980s, the techniques for developing crystals during firing have received new attention from studio potters in different parts of the world.
Crystals are formed under different conditions in nature and are recognized as, for example, salt crystals, snowflakes and precious stones. Crystals fulfill crucial functions in modern technology and are used in mobile phones, televisions and computers, among other things. Since the natural supply of crystals does not cover the need, crystals are grown for specific purposes in commercial laboratories. Ceramics working with crystalline glazes use similar techniques: specific substances are mixed, heated to high temperatures and then cooled at a controlled pace.
Crystalline glazes contain zinc oxide, silica and various combinations of other substances. The size of the crystal depends on two factors: the pace of cooling in the oven and the amount of crystal-forming substances in the glaze mixture. When the glaze cools quickly, small crystals are formed. With slower cooling, the crystals become larger. Crystals can be divided into micro crystals, which can only be seen through a magnifying glass, and macro crystals which are visible to the eye.