Temper, thermal shock and cooking pots: A study of tempering materials and their physical significance in prehistoric and traditional cooking pottery

Abstract

Prehistoric and traditional ceramics contain a wide range of tempers (non-plastic inclusions), including sand, sherd (grog), sponge spicules, phytoliths (siliceous bark ash), diatomite, organic fibers, shell, calcite, mica and asbestos. The use of these materials in traditional and archaeological ceramics and their association with cooking pottery and thermal shock resistance are examined. The thermal shock parameters that are relevant to low-fired ceramics are identified and tested. The primary factor in the thermal shock resistance is identified as fracture toughness. By increasing the amount and size range of temper additions, and by selecting tempers that are platy and fibrous, fracture toughness can be enhanced. Secondary factors include porosity, thermal expansion and relative strength. These parameters are tested employing fracture energy and thermal expansion measurements, and quench tests.