Ultra close-range photogrammetry to assess the roughness of the wall painting surfaces after cleaning treatments

In the present work authors show the results obtained by means of the application of ultra closerange photogrammetry for assessing the pattern of a detached wall painting's surface during/after cleaning treatments. The cleaning treatments are critical operations in conservation so the choice of the method and the definition of the protocol require preliminary activities and studies for the optimization of the procedure. Since the removal of the material is an irreversible operation, an extremely selective method is needed. The criteria traditionally chosen for the selection of the adequate cleaning procedure are the evaluation of the amount of material removed during the treatment and the surface variations (roughness) before and after the treatment. A non-destructive technique could be particularly highlighted as an assessment tool; to this aim the authors propose the photogrammetry method in ultra close-range mode. The ultra close-range photogrammetry is a total non-invasive method, fully portable, and easy to use. The cleaning treatments studied in this work are chemical cleaning, and laser cleaning. The obtained information on the third dimension of the surface by means of ultra close-range photogrammetry was compared with results performed by 3D optical microscope (only on selected single points). The colorimetric information on selected areas during and after the cleaning completes the surviving activity. The performed tests on the case study demonstrate the ability of the proposed approach to control the effectiveness of the cleaning procedures applied on wall paintings during conservation interventions. The advantages due to the portability and to the non-destructivity of photogrammetry (no-contact measurement method) with regard to others techniques candidates, led this methodology to be used in wider restoration works.