Valerie Addicott

 

Georgia Pottery

Valerie Addicott

 

About The Clay Process

 Clay

The clay that I use is a high fired stoneware or porcelain fired in a gas downdraft kiln to a cone 10 using a gas reduction fire of 2380 degrees Fahrenheit. This is the most desirable of all firings due to the depth of colors, it is also the most unpredictable of firings and can be very difficult to reproduce the same effects. The two types of clay bodies that I use are dense enough that the clay particles fuse together at 2300-2400 degrees Fahrenheit (hence the name "stoneware"). These clays are water-tight and very durable which make wonderful utilitarian pieces. Stoneware clays are great for baking, as they transmit heat evenly through the clay and retain the heat for an even and consistent bake.

Bisque Firing
 

When completely air-dried slowly over several days, the pottery is bisque fired at a relatively low temperature, around 1830 degrees Fahrenheit, to make the clay ready for glazing. Bisque firing removes still more moisture out of the clay and makes the clay firm enough to handle, yet porous enough to absorb the liquid glaze. Bisque firing temperatures are similar to temperatures used for "low-fire" pottery, such as red clay garden pots and bricks. After bisque firing, stoneware and porcelain are ready to be glazed.

Glazing

This is the most complicated and difficult part of the production of my pottery. Glazes are not pigments like paints that allow you to select a color by looking at the raw glaze. Glazes are refined chemicals, usually mineral oxides, that are mixed in a chemical formula that will allow the glaze to "flux" (melt) at a certain temperature, much like glass. Chemicals added to glazes to add color to the pot include copper, cobalt, iron, and rutile. Glaze formulas are often "proprietary," meaning a potter who has developed a certain color or look over years of experimentation will not share that information with other potters.

Each layer of glaze thickens the glaze on the pot. If glazes are applied too thickly, the glazes will melt and frequently flow more than planned during the glaze firing. When this happens, the glazes will run right off the pot and onto the shelf, and as the kiln cools, the pot is stuck to the shelf and in most cases both the pot and the expensive kiln shelf are ruined. This makes for a very expensive mistake.

Each glaze base is a powder which is mixed with water, until the desired density or thickness is obtained. This density is measured regularly during each glazing process, to ensure that the glaze will be the right thickness when applied to the pots. Pots can be dipped in the glaze, or glaze can be poured over the pot, or the glaze can be brushed or sprayed onto the pot - all these techniques produce different effects.

Glaze firing

Glaze firing can be done in either an electric kiln or a gas kiln. Depending on which type of kiln is used, the difference in the appearance of a glazed pot can be quite astounding. Electric kilns require oxygen to be present through the entire firing process (oxidation firing). Gas kilns allow the potter to control the oxygen level that mixes with the natural gas during the firing. Reducing the air flow at designated intervals for a short period of time (reduction firing) changes the atmosphere in the kiln and affects the glaze chemicals, producing the vivid "copper reds" and the soft, deep blues, lavenders, purples, and greens. 

The glaze firing takes 3 days to complete. On the first day the kiln is loaded. That night the kiln is "candled" (allowed to sit at a very low temperature to finish the drying process). On the second day, the kiln is fired, usually to temperatures between 2350 and 2400 degrees Fahrenheit, a process that normally takes 10 to 12 hours, after which the kiln is left to cool very slowly for 24 to 48 hours or until the inner tem is below 300 degrees before opening. On the last day, the kiln is slowly opened over a period of 3 to 4 hours, as the pots continue to cool to handling temperatures.

The pots are finally removed from the kiln the afternoon of the third day. Pots that are cooled too rapidly will shatter. Once pots are removed from the kiln and brought back into the studio, the unglazed edges are sanded, and the pots are ready for sale.

Care of your Stoneware

To use in your oven, place the piece in a *cold* oven. Do not use on a burner of your stove. The biggest thing is to avoid thermal shock and let the stoneware heat up with the oven. This stoneware is safe for microwave, dishwasher, oven and freezer [but return to room temperature before reheating].

 

 

       

 

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