Blue Ridge Pottery - Glazing

Glazing: (In the case of pottery) the covering of the clay pot with a glass coating in order to seal it and make it a hard easily cleaned surface.

Glazing is by far the most difficult part of our entire process. The chemistry is very exact and glaze formulas must be measured out on a gram scale to a three decimal place accuracy. Many factors can affect our firings. These include such things as air temperature and oxygen content, wind, humidity and evaporation rate in our propane tanks. Kiln design and firing is both an art and a science and we still never know the quality of our load until we open the kiln. Potter’s are lucky they get to have Christmas (kiln opening) once or twice a week.

Silica – The building block of the World.

The basic element in glazing is glass and the basic element in glass is silica. Silica is found in various forms in many of the rocks on our planet. Sand is mostly comprised of silica. Silica in the form of glass makes our glasses, our windows, and is a part of every computer you are reading this on.

When powdered silica is heated to approximately 2300 degrees, along with certain additives, it melts and as it cools it becomes glass. Many people do not understand that glass is a liquid, not a solid, even when cooled in the form of our windows or eyeglasses.

“How do you get these colors and patterns?"

Many people ask us “How do you get these colors and patterns?”. In our glaze recipes are a number of other clays and silica bearing materials as well as oxides which are whiteners and colorants. The whiteners include chemicals like zinc oxide, titanium dioxide and tin oxide. The colorants include chemicals such as copper carbonate (red and green), cobalt carbonate (blue and purple), and elements like zinc oxide and iron oxide to enhance color and grow crystals.

When we put glazes on the pieces before they are fired they have almost no color. It is not until the pieces are fired in the kiln that the color manifests. So what happens in the kiln? Our kilns are especially designed to create a condition of negative oxygen. So what is negative oxygen? In effect, we put more gas into the kiln than we are putting in oxygen to burn it. This red hot gas is looking for oxygen and the only available oxygen in the kiln is in the oxides mentioned above. Over a period of about ten hours this reduction process continues to change the chemical composition and color of the piece.

Also see: Glazes, & Our Kilns