Microscopic Studies of Stone Alteration Products: From Field to Lab

Stone in the built environment show diverse decay features related to the interaction of its characteristics with the environment (see [1] for a brief review). The characterization of these decay features is important for the diagnosis of their causes and for determining the intervention strategies. Several microscopy techniques have been used for these goals [2]. Here are discussed some main issues related to the use of microscopy techniques for the characterization of decay features. The first issue to consider concerns sampling. Digital cameras allow for field observations near the stereomicroscopy level, favouring some characterization without sampling as in Figure 1a that suggest the preference of salt efflorescences for contacts along grains and mica crystals, possibly due to porosity structures. In Figure 1a, one can also see that the efflorescences are formed by small granular crystals (see SEM observations in Figure 1b) and it is possible to distinguish some particles that are near micrometric size. While lighting conditions and focusing distance can impose limitations in the observation distance, the increase in image quality suggests that in the very near future observations at the stereoscopic level could be performed easily and cheaply in situ. However, in general, and namely for chemical studies, microscopic studies involve some removal of material and in that sense are somehow destructive. This can be less relevant in the case of sampling decay products (resulting from alteration of original materials) but it is necessary to consider the impacts of the sampling procedures on the original materials and the potential interest of the preservation of the alteration products. Some aspects can minimize the impact of sampling:!!...!!