Pyrometric cones measure heat-work (the effect of time and temperature). They are slender pyramids made from about 100 carefully controlled compositions. Each cone number is unique in measuring temperature within a small temperature range (less than 30°C). Cones measure the amount of heat absorbed over time. As the cone nears its maturing range, it softens and the tip begins to bend, drawn down by the influence of gravity.
Standard, or Large cones are used as witness cones to monitor the firing and verify temperature uniformity. A cone pack is necessary to support the cones during firing. If you have a kiln sitter on your kiln, you should use Junior cones.
Warning! Do not view cones above earthenware temperature with the naked eye as this may cause cataracts. View through welders goggles - sunglasses are not suitable as they filter out UV, but not the infra-red, which is the damaging wavelength in this case!
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