Salt Glaze Firing
Salt glaze pots are highly functional. They are durable, waterproof, and greatly lend themselves to everyday use for food and presentation.
The process of salt glazing was discovered in Germany in the 15th Century. The English brought the practice to America in the 1700’s, where it became a popular firing technique for early American crocks, jugs, and other functional pottery.
Most of my salt glazed work is hand painted using powdered metals such as titanium, rutile, iron, and cobalt, mixed with water. I do not apply glaze to the outside of the pots. First, I bisque fire both porcelain and stoneware pottery to 1,800 degrees in my electric kiln. After this, I glaze the insides with a liner glaze. The liner glaze is a mixture of glass forming chemicals that will become a glossy surface inside of the pot making it easy to clean, and is aesthetically pleasing. The pots are lined with this glaze because the vapors that form during a salt glaze firing do not always get inside of the pots during the firing. The pots are then loaded into the gas-fired kiln, on silicon carbide shelves that withstand both the high temperature and the corrosive nature of the process. Each piece is placed on wads of a clay mixture of kaolin and alumina hydrate to prevent them from fusing to the shelves.
Once the kiln is heated to 2,300 degrees (cone 9*), I begin putting rock salt into the bottom of the kiln, which immediately vaporizes into a heavy white cloud. Some of the sodium from the sodium chloride reacts with the silica in the clay body, forming sodium alumina silicate—which is essentially a textured, transparent layer of glass on the surface of the pots. I usually put the salt into the kiln 3 times during a firing. The third addition of salt goes in around 2,360 degrees (cone 11). After this I shut the kiln off and let it cool for two days.
The glaze in this process is unique in that instead of fusing a glaze onto the surface of the clay, the glaze is actually part of the clay. I fire most of my work using this technique for both function and aesthetics.
*When I speak of cones, they are ceramic cone-shaped objects that are chemically manufactured to melt at specific temperature and heat saturations. They are placed on the shelves inside of the kiln during the firing, allowing me to look into the kiln and gauge the temperature by the melting or "bending" of the cones. Technically they are called Pyrometric Cones and have numbers assigned to them that correlate to specific temperatures.
Salt glaze pots are highly functional. They are durable, waterproof, and greatly lend themselves to everyday use for food and presentation.
The process of salt glazing was discovered in Germany in the 15th Century. The English brought the practice to America in the 1700’s, where it became a popular firing technique for early American crocks, jugs, and other functional pottery.
Most of my salt glazed work is hand painted using powdered metals such as titanium, rutile, iron, and cobalt, mixed with water. I do not apply glaze to the outside of the pots. First, I bisque fire both porcelain and stoneware pottery to 1,800 degrees in my electric kiln. After this, I glaze the insides with a liner glaze. The liner glaze is a mixture of glass forming chemicals that will become a glossy surface inside of the pot making it easy to clean, and is aesthetically pleasing. The pots are lined with this glaze because the vapors that form during a salt glaze firing do not always get inside of the pots during the firing. The pots are then loaded into the gas-fired kiln, on silicon carbide shelves that withstand both the high temperature and the corrosive nature of the process. Each piece is placed on wads of a clay mixture of kaolin and alumina hydrate to prevent them from fusing to the shelves.
Once the kiln is heated to 2,300 degrees (cone 9*), I begin putting rock salt into the bottom of the kiln, which immediately vaporizes into a heavy white cloud. Some of the sodium from the sodium chloride reacts with the silica in the clay body, forming sodium alumina silicate—which is essentially a textured, transparent layer of glass on the surface of the pots. I usually put the salt into the kiln 3 times during a firing. The third addition of salt goes in around 2,360 degrees (cone 11). After this I shut the kiln off and let it cool for two days.
The glaze in this process is unique in that instead of fusing a glaze onto the surface of the clay, the glaze is actually part of the clay. I fire most of my work using this technique for both function and aesthetics.
*When I speak of cones, they are ceramic cone-shaped objects that are chemically manufactured to melt at specific temperature and heat saturations. They are placed on the shelves inside of the kiln during the firing, allowing me to look into the kiln and gauge the temperature by the melting or "bending" of the cones. Technically they are called Pyrometric Cones and have numbers assigned to them that correlate to specific temperatures.
