Overfired

Overfired is an adjective used to describe a heating process or product that has been heated beyond the intended or safe temperature. It is most commonly associated with kilns, furnaces, or burners where heat input exceeds design limits, causing changes in materials and sometimes damage.

In ceramics, overfiring occurs when a piece is heated past the maturity point of the clay body or glaze. The results can include color changes, warping, blistering, pinholing, glaze running or crawling, and in extreme cases, deformation of the ceramic body. In metalworking and heat treatment, overfiring can alter grain structure, reduce hardness, promote unwanted phase changes, or cause deformation from excessive thermal expansion.

Other contexts include glassmaking and industrial furnaces, where excessive temperature can cause devitrification, defects in glass, or increased oxidation and scaling on metal surfaces. Overfiring is often linked to control failures, such as faulty sensors, incorrect heating schedules, or loading patterns that impede even heat distribution.

Detection and prevention rely on accurate temperature monitoring and process control. Techniques include using calibrated controllers, installing reliable thermocouples, and employing witness cones in kilns to indicate actual peak temperatures. Regular pretests, piece-specific firing schedules, proper loading to ensure even heat transfer, and routine maintenance of heating equipment help minimize the risk of overfiring. If overfiring occurs, the affected items may be permanently damaged, and energy waste can increase due to extended or repeated cycles.