Structural collapse in kaolinite, montmorillonite and illite clay and its role in the ceramic rehydroxylation dating of low-fired earthenware

• Structural collapse of clay tracked by infrared spectroscopy.
• Activation energies determined for different clay firing temperatures.
• Prehistoric earthenware ceramics fired below 900 °C.

The rehydroxylation dating of ancient pottery estimates the age of ceramic manufacture based upon the total hydroxyl (OH) accumulation since initial firing. The diffusion of OH is impacted by the structural porosity of the ceramic that becomes progressively, or suddenly, closed with increasing temperature as the clay structure collapses. Changes in ceramic mineral structure along the temperature continuum occur at certain thermal set points. Infrared spectroscopic analysis of heat-treated kaolin, illite, and montmorillonite reveals that shifts in the Si-O band correlate with the extent of structural collapse occurring between 600 and 1000 °C. Accelerated rehydroxylation experiments reveal that the activation energy of rehydroxylation decreases with greater structural collapse and indicates that the rate of rehydroxylation will be faster for ceramics fired at more elevated temperatures.