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offcntrI occurs to me, I talk about what cone I'm firing to regularly on this blog, but have never actually shown you the cones.
Pyrometric cones are devices designed to accurately measure heat work in a kiln. Heat work, the interaction of time and temperature in a firing, is more useful than ambient temperature, which can be measured with a thermocouple and pyrometer. (A thermocouple is usually two different metal wires, twisted together or joined at the tip, that generate an electric current proportional to temperature. A pyrometer takes that current and converts it into a read-out, usually digital these days, calibrated to degrees in your preferred scale.) Because pottery materials respond not just to how hot it is, but how long it's been and how fast the temperature is rising. cones provide much more useful information to the potter than a pyrometer.
The idea goes all the way back to Josiah Wedgwood, back in 1782, who used beads of different compositions to determine how his work was faring in the kiln. Hermann Seger perfected the cone for the Royal Porcelain Factory in Berlin, in 1886. Seger cones are still made today, but most potters us Orton cones, ranged on a standardized scale and manufactured since 1896 by the Edward Orton Company in Columbus, Ohio.
The original Orton cones were numbered from 1 to 14; as low-temperature applications became more common, a new range was added. Rather than using negative numbers, they added a "0" to the beginning of the number. Larger "0" numbers denote lower firings, running from 01 (pron. "Oh-One") down to 022. There is no cone zero.
Lower temperature cones are all brown, from iron oxide in the mix. Because iron oxide is refractory (resists melting) in oxidation, but fluxing (promotes melting) in reduction, they're not super accurate in gas firings, but do well enough for my purposes. For many years, all the other cones were all white, which led to adventures like the time at a summer pottery workshop where the instructor put the cone packs together without his reading glasses. One part of the kiln leapt ahead in temperature, late in the firing, and we fiddled with the damper, air and oil supply until the other part caught up. (We later discovered he'd put both cone 8's in one pack, 9's in the other.) In the last decade or so, Orton has color-coded their cones, though the organic die will burn out in the firing.
I use eight cones in each cone pack, in two rows, pointing opposite directions. The lower temperature cones are closest to the peephole; once they've melted/dropped, I can see the hotter cones behind them. There are two peeps in the door, one about 6 inches from the bottom, the other 10-12 inches from the top.
My cone packs, in order from low to high, are 08 (when I do body reduction), 04 (check the chimney for flame), 1 (progress), 4 (more for reassurance than anything), 8 (is the kiln firing evenly? Fiddle with the damper!), 9 (fiddle some more!), 10 (that's it, we're done), 11 (oh shit, what happened?). They're boat shaped, with sideboards, because by the time we finally reach cone 10, the lower cones are completely liquid, and we do not want them spilling out onto the shelves.
Pyrometric cones are devices designed to accurately measure heat work in a kiln. Heat work, the interaction of time and temperature in a firing, is more useful than ambient temperature, which can be measured with a thermocouple and pyrometer. (A thermocouple is usually two different metal wires, twisted together or joined at the tip, that generate an electric current proportional to temperature. A pyrometer takes that current and converts it into a read-out, usually digital these days, calibrated to degrees in your preferred scale.) Because pottery materials respond not just to how hot it is, but how long it's been and how fast the temperature is rising. cones provide much more useful information to the potter than a pyrometer.
The idea goes all the way back to Josiah Wedgwood, back in 1782, who used beads of different compositions to determine how his work was faring in the kiln. Hermann Seger perfected the cone for the Royal Porcelain Factory in Berlin, in 1886. Seger cones are still made today, but most potters us Orton cones, ranged on a standardized scale and manufactured since 1896 by the Edward Orton Company in Columbus, Ohio.
The original Orton cones were numbered from 1 to 14; as low-temperature applications became more common, a new range was added. Rather than using negative numbers, they added a "0" to the beginning of the number. Larger "0" numbers denote lower firings, running from 01 (pron. "Oh-One") down to 022. There is no cone zero.
Lower temperature cones are all brown, from iron oxide in the mix. Because iron oxide is refractory (resists melting) in oxidation, but fluxing (promotes melting) in reduction, they're not super accurate in gas firings, but do well enough for my purposes. For many years, all the other cones were all white, which led to adventures like the time at a summer pottery workshop where the instructor put the cone packs together without his reading glasses. One part of the kiln leapt ahead in temperature, late in the firing, and we fiddled with the damper, air and oil supply until the other part caught up. (We later discovered he'd put both cone 8's in one pack, 9's in the other.) In the last decade or so, Orton has color-coded their cones, though the organic die will burn out in the firing.
I use eight cones in each cone pack, in two rows, pointing opposite directions. The lower temperature cones are closest to the peephole; once they've melted/dropped, I can see the hotter cones behind them. There are two peeps in the door, one about 6 inches from the bottom, the other 10-12 inches from the top.
My cone packs, in order from low to high, are 08 (when I do body reduction), 04 (check the chimney for flame), 1 (progress), 4 (more for reassurance than anything), 8 (is the kiln firing evenly? Fiddle with the damper!), 9 (fiddle some more!), 10 (that's it, we're done), 11 (oh shit, what happened?). They're boat shaped, with sideboards, because by the time we finally reach cone 10, the lower cones are completely liquid, and we do not want them spilling out onto the shelves.