For less than the cost of a can of soda, a set of Orton Ceramic Pyrometric Cones placed in each kiln firing will provide you with the assurance that you fired your ceramics properly.
Electronic controllers rely on an electrical output generated from a thermocouple inserted into the kiln. A thermocouple is made by welding two metallic wires together. The bead that forms by welding the two wires is placed into the kiln. When the welded bead is heated, it will create a small voltage that can be measured. The controller measures the voltage and converts the signal to a representative temperature. Several changes occur every time the thermocouple is heated and cooled. These changes cause the voltage signal to shift. The typical result of this shift results in a lower than actual temperature within the kiln.
Electronics are not foolproof. They need to be calibrated to insure they are operating within performance criteria. Use of a cone to verify the calibration of the electronic controller is a simple and effective insurance device to prove that the kiln did its job. The Orton Ceramic Pyrometric Cones are standardized to perform the same with each batch made, and are not subject to the degradation and changes that occur with electronics. Most kiln manufacturers, clay producers and glaze manufacturers advocate the use of cones in each and every firing.