The high temperatures achieved by kilns bake clay pieces into ceramics. Part of that process is ensuring the clay pieces absorb enough of the heat from the kiln in order to transform them. The amount of time it takes for the pieces to absorb this heat energy is measured by cones. Simply stated, a cone is a measurement of the amount of time it takes a cone of clay to absorb the proper amount of temperature necessary to transform it into a ceramic. Kilns are designed to heat and cool slowly, so it is necessary to be able to measure heat absorption accurately. Actual cones of clay are placed in the kiln and can be seen from the outside. Once the cones have absorbed the proper amount of heat, the kiln is turned off and allowed to cool slowly. At this point, the clay pieces have been heated correctly and become ceramics.