Micro-Raman mapping on polished cross sections: a tool to define the penetration depth of conservative treatment on Cultural Heritage

Nowadays, in order to preserve the surfaces of works of art, several organic and inorganic substances are used. To evaluate the penetration depth and the distribution of these substances inside thematerials, it is essential to define the effectiveness of a conservative treatment. Owing to the ambiguous results obtained with the current analytical techniques, the achievement of this aim is critical. This study shows how micro-Raman mapping on polished cross section is an effective tool capable of investigating the inner portions of the materials. A set of painted plasters has been treated with ammonium oxalate solutions, an inorganic substance widely used for conservation works of carbonatic materials. The micro-Raman mapping of the lines of the newly formed calcium oxalate allowed correlation of the penetration depth and the distribution of the product inside the specimens with different conditions of treatment. Moreover, a good agreement between micro-Raman spectroscopy and microscopic techniques has been obtained.