ESEM and Video Microscopy Studies in Stone Conservation

Abstract

Observation of stone deterioration using in situ,time-lapse microscopy techniques has revealed previously undescribed material behaviors that help to explain the destructive effects of several important processes in wall paintings, historic structures and monuments. It has long been acknowledged that cyclic stresses imparted by humidity changes, wet-dry cycling, and the crystallization and hydration of soluble salts, are important agents in the deterioration of these porous structures. The crystallization of salts is a particularly serious conservation problem (Arnold, 1975). Over time, cyclic salt crystallization results in the physical breakdown of the material (Goudie, 1993). Objects affected by such processes are often difficult to conserve since they are weak to begin with and the presence of salt inhibits the curing of some common conservation materials (Price and Kumar, 1994).Sodium sulfate is one of the most damaging of salts, apparently because it expands during the transition from the anhydrous phase (Na2SO4; thenardite) to the decahydrate form (Na2SO4•l0H2O; mirabilite).