Field microscopy applied to the understanding of the technology and conservation of wall paintings

Wall paintings are complex, heterogeneous structures open to the environment and composed of multiple layers. Additionally, they are frequently located in remote areas, where basic infrastructure is not available. The causes and mechanisms involved in the complex deterioration phenomena, which wall paintings are often subjected to, are therefore difficult to identify and address. Developments have been made to target conservation issues in situ with non-invasive and portable investigative techniques, however standard practice to investigate stratigraphic information still involves analysing samples in a laboratory setting. In remote sites this approach is inefficient, as in many cases decisions on treatment cannot wait for the results of the laboratory examinations. This may have serious consequences on the integrity of the painting. This paper describes adaptation of classical methods for the in-situ preparation of cross-sections, thin-sections and dispersions utilising custom-made equipment. The methodology allows for a direct examination of samples in-situ, using a portable polarizing microscope (field microscopy). The system was adapted and developed to not only capture incident and transmitted light, but also to capture multispectral images (infrared-, ultraviolet-reflected and ultraviolet- and visible-induced luminescence), using external radiation sources. Comparisons with benchtop equipment are made to demonstrate the efficacy and usefulness of the process.