Abstract
The assessment of five different laser treatments in the conservation of wall paintings was devised on the basis of the surface temperature monitoring by infrared thermography (IRT), ultraviolet-induced fluorescence-visible (UV-VIS) imaging, and optical coherence tomography (OCT). A series of yttrium-aluminum-garnet (YAG) lasers were tested for removal of shellac layers from wall painting mock-ups. The mock-ups were realized as buon fresco with different mineral based pigments (earths and iron oxide) on a lime- and sand-based mortar. After the carbonatation process, all the samples were treated with shellac (5% in ethanol). The effects of neodymium (Nd):YAG, holmium (Ho):YAG, and erbium (Er):YAG laser sources, in different operative modes, on average temperature of the surface, color, and morphology were inspected with complementary sensors. The results show the necessity to adopt a combined approach in establishing safe laser operating conditions to avoid any undesired effects induced on the artefacts by the laser treatments. We demonstrate, for the first time, the performance of the Ho:YAG laser in the removal of a conservation treatment.
Highlights
VillanuevaThe cleaning is an irreversible restoration intervention on cultural heritage assets involving the removal of unwanted substances generally deposited on the surface of the object
The image was produced by processing the visible region spectral dataset acquired with the VIS-NIR multispectral scanner, collected
Three YAG lasers—doped with Nd, Ho, and Er ions—emitting, respectively, at 1064, 2100, and 2940 nm were tested for the removal of a shellac layer from mural painting mock-ups
Summary
The cleaning is an irreversible restoration intervention on cultural heritage assets involving the removal of unwanted substances generally deposited on (or embedded into) the surface of the object. The decision as to what material should be preserved or removed is crucial for planning the restoration, along with the definition of the most appropriate methods to carry out a selective, effective and safe cleaning. These choices imply a proper knowledge of the artwork’s materials and history, as well as of the expected performance of the cleaning methods. The target for the restorer is to exploit the most suitable techniques and their combination in order to guarantee the best possible results in terms of cleaning intervention
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