During several hundred years of burial in the soil, glasses, especially those with medieval compositions, develop heavily corroded surfaces, showing phenomena such as local pitting, laminated layers and browning effects. For this study the damage phenomena have been characterised for three original glasses, using conventional methods (light microscopy and SEM of the surface and cross sections) and microfocus X-ray computed tomography (mCT), a new non-destructive analytical technique.
The degradation of glass in the soil depends on a variety of parameters, concerned with the glass itself and with the burial environment. Since synergetic effects may complicate any mechanistic studies, laboratory experiments have been carried out under controlled conditions.
Humid soil environments with a pH of 6.5 to 7.5 lead to the development of local microcracks on the surface, whereas more alkaline soil conditions (pH 8.0 to 9.0) favour the formation of laminated structures. The conclusions of the paper focus on the effect of glass composition (model glasses and archaeological glasses), soil conditions (variation of pH) and exposure time (23 months versus several centuries).