Evaluation of the chemical and physical changes induced by KrF laser irradiation of tempera paints

A systematic study of the chemical and physical changes induced by exposure to UV (248 nm) excimer laser light of unvarnished tempera paint samples has been undertaken as a part of the research activities included in the European project "Advanced workstation for controlled laser cleaning of artworks". The direct exposure of the paint to the UV laser configures the worst case scenario of laser cleaning, as a thin protective layer of varnish is normally left to minimize the dose of UV radiation that reaches the paint surface. However, in the practice of laser cleaning, there is a need to characterize and quantify the possible effects of direct UV laser irradiation of unvarnished paints. To this purpose, a broad range of techniques have been used including profilometry, colorimetry, optical and vibrational spectroscopic techniques, such as laser-induced fluorescence (LIF), laser-induced breakdown spectroscopy (LIBS), Fourier transform Raman (FTR) and infrared (FTIR), and analytical mass spectrometric techniques, like direct-temperature-resolved mass spectrometry (DTMS) and laser desorption and ionization time of flight mass spectrometry (LDI-TOF). Integration of the results obtained by these techniques allowed the investigation of the nature and degree of change of the irradiated paint systems. These were observed to strongly depend on the type of paint system.

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