Fahrenheit 2200 or bust
Pots are often fired two times. The first, or bisque firing, is to bake out the impurities from the clay which will also undergo a chemical transformation where the dried clay will no longer slake back into wet clay when exposed to water. This firing is to 1800 degrees Fahrenheit. The second firing, to 2200 degrees, takes place after Darlene applies the glazes.
Oxidation vs. reduction
In addition to the glaze composition, what a pot looks like is determined by how they are fired-- oxidation or reduction. Oxidation firing most often uses electricity to reach the glass melting temperatures. Reduction, on the other hand, uses combustible fuels such as gas or wood. In this process, oxygen can cut off or "reduced" which effects the chemical properties of the glazes. For example, copper in oxidation firing will turn green-- think green patina. Yet, if the oxygen is burned out during the process,then the copper will turn red because the metal doesn't bind with the oxygen.
Glaze colors
As noted different metals and minerals can be added as colorants. They can also be used to change the texture of the glazes. Here is a table of materials Darlene uses to attain different colors:
| Material | Color |
|---|---|
| Copper | Greens |
| Cobalt | Blues |
| Iron | Browns |
| Rutile (>90% Titanium dioxide) |
Yellows |
Mixing these chemicals in varying percentages can alter the colors. In the example on the glazing pots page, Iron and Rutile combine to make a tan.
Out of the kiln
Each of these firings can take a day or more for the full cycle. For example, the glaze firing is 12 hours heat up and a 12 hour cooling cycle. When the kiln is finally cool, unpacking the glaze load is a real treat as you never know exactly how any given piece is going to turn out. This is especially true for Darlene who loves to experiment with her glazes.
Check out the pots
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The kiln fires to 2200F over a 12-hour period. You can see the orange glow of 2069F just under the lid and in the peephole.
Peering in the peephole you can see the "cone" which melts when the kiln hits the right temperature. A good check for the digital temperature readout.
After another 12 hours of cooling, Darlene finally gets to open the kiln.