Pottery glazing has been around for almost as long as the human race. It is unknown exactly when people first started glazing their pottery, but most archeologists agree that it was sometime between the 9th and 8th century B.C. Since then glazing has been used to keep many different styles and compositions of pottery waterproof and decorated. Many of the glazing methods used today have their roots in the ancient glazing methods.
Earliest Glazing
The earliest discovery of glazed pottery came from the 8th or 9th century B.C. or even earlier. Early glazing was discovered in China, Egypt, Mesopotamia and Greece. Each country seemed to have a particular style of glazing that was preferred. Egyptian glazing was largely alkaline based, as was that used in China and Mesopotamia. Greece and Rome used lead glazing or clay glazing. From these early instances of glazing come the modern glazing practices that are in use today.
Alkaline Glazing
Alkaline glazing employs some of the earliest forms of pottery glazing. A variety of materials were used to make the glazes. In Mesopotamia, ash was mixed with sand to create the surface glaze over the pottery constructed in that area. Another ancient alkaline glazing method used soda and sand. Greek glazing was created using extra clay particles themselves. Some modern glazes still use alkaline bases for their finishes.
Lead Glazing
Lead glazing was first used by the Romans from around the 1st century B.C. A mixture of lead oxide and sand was placed over the pottery before it was fired. Lead glazing was used for thousands of years after the Romans first used it, but within the last 200 years has fallen out of favor due to the potentially harmful effects of lead, although lead glazing is still practiced in some areas.
Tin Glazing
Tin glazing was introduced around 1100 A.D. in Persia. Tin glazing was used as an alternative to porcelain, and pottery fired with tin glazing took on an opaque, white cast. Mixtures of kaolin and veldspar clays created the tin content necessary to cover the pottery in a coating of white. Tin glazing became very popular during the Renaissance period and fell out of favor with the introduction of enamel glazing in the 1700s, which could be fired at lower temperatures.
Modern Glazing
Modern glazing is created by a mixture of glass particles and colored oxides. Glass powder is brushed onto the surface of the pottery, then heated to extreme temperatures to melt the glass powder over the glaze. Modern glazing has advanced far enough to provide thousands of different glazing combinations and appearances.