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Glazing This is the most complicated and difficult part of the production of 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 "propietary," meaning a potter who has developed a certain color or look over years of experimentation will not share that information with other potters. |
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At Mud in Your Eye, we use over a dozen glazes, with at least two glazes and often as many as four glazes on a pot. This can be a very tricky process, since each layer of glaze must be applied fairly thinly. 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. |
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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. |
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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, lavendars, purples, and greens that you see so much around our shop. |
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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 temprature 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 overnight 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. |
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