Technical Jiggery-Pokery
Aug. 12th, 2014 08:35 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
offcntrIf I'm gonna throw technical terms around, I should probably define a few of them. Consider this your reference section.
Temperature. Degrees Fahrenheit, or Celsius. Temperature of the thermometer or thermocouple persuasion isn't that useful in determining the progress of your firing. Clay and glazes melt as a function of time and temperature. If you raise the temperature of the kiln slowly, your pots will mature at a lower temperature than if you fire fast.
Cones. Pyrometric cones are formulated from a mixture of clay and glaze minerals to melt at a specific temperature given a measured rate of firing. Or, simply put, they melt the same way your pots do, so by watching them in the peephole, you can tell how close to finished you are.
Cone 08, cone 8, cone 10. Different heat points in the firing. Cones with a zero in the number (read "cone oh-eight") are negative numbers, so cone 08 is 15 cones cooler than cone 8 (because there's no cone 0. Go figure). Cone 08 is when I do body reduction, cone 10 is when I shut off the kiln.
Reduction. In a fuel burning kiln--gas, oil, wood--the amount of oxygen in the kiln can be adjusted to get clay and glaze color effects. Most commonly, by reducing the amount air in the kiln at critical points, you can make iron spots appear in the clay, and make iron glazes green or blue, copper glazes red. This is called a reducing atmosphere, or reduction.
Body reduction. Reducing atmosphere at an early stage of the firing, before the glaze seals over. This allows you to reduce iron in the clay itself, which comes to the surface in the iron spots that freckle the surface of most stoneware clays.
Oxidation. The opposite of reduction. Makes my glazes white and unattractive, so I try to avoid this. I'm not always successful, because old kiln haz air leaks.
Damper. The kiln shelf that slides in and out of the chimney to control the amount of air drawn into the kiln (draft). Closing the damper creates reduction.
Temperature. Degrees Fahrenheit, or Celsius. Temperature of the thermometer or thermocouple persuasion isn't that useful in determining the progress of your firing. Clay and glazes melt as a function of time and temperature. If you raise the temperature of the kiln slowly, your pots will mature at a lower temperature than if you fire fast.
Cones. Pyrometric cones are formulated from a mixture of clay and glaze minerals to melt at a specific temperature given a measured rate of firing. Or, simply put, they melt the same way your pots do, so by watching them in the peephole, you can tell how close to finished you are.
Cone 08, cone 8, cone 10. Different heat points in the firing. Cones with a zero in the number (read "cone oh-eight") are negative numbers, so cone 08 is 15 cones cooler than cone 8 (because there's no cone 0. Go figure). Cone 08 is when I do body reduction, cone 10 is when I shut off the kiln.
Reduction. In a fuel burning kiln--gas, oil, wood--the amount of oxygen in the kiln can be adjusted to get clay and glaze color effects. Most commonly, by reducing the amount air in the kiln at critical points, you can make iron spots appear in the clay, and make iron glazes green or blue, copper glazes red. This is called a reducing atmosphere, or reduction.
Body reduction. Reducing atmosphere at an early stage of the firing, before the glaze seals over. This allows you to reduce iron in the clay itself, which comes to the surface in the iron spots that freckle the surface of most stoneware clays.
Oxidation. The opposite of reduction. Makes my glazes white and unattractive, so I try to avoid this. I'm not always successful, because old kiln haz air leaks.
Damper. The kiln shelf that slides in and out of the chimney to control the amount of air drawn into the kiln (draft). Closing the damper creates reduction.