New insights into the effects of Yb-doped fiber laser on tempera paintings: Influence of the pigment and binder

Proper Optimization of laser parameters (frequency, energy, fluence) is essential when cleaning tempera paintings to avoid physical, chemical, or mineralogical damage to the original paint layers. While these parameters are well-studied for solid-state lasers, little is known about fiber lasers, which offer notable advantages such as portability, resistance to shocks, high repetition rates, and adjustable scanning areas. In this study, a Yb-doped fiber laser (1064 nm, 30 ns pulse, 10 m/s scan speed, rectangular spot) was applied to pure pigment powder (azurite, malachite, orpiment, cinnabar, white Kremser) and to tempera paints prepared with the pigments mixed with egg yolk or rabbit glue. A treatment protocol was developed to examine how frequency and pulse energy influence the pigments' and temperas' response to irradiation. Post-treatment evaluation using stereomicroscopy, colour spectrophotometry, attenuated total reflection-Fourier-transform infrared spectroscopy, micro-X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy revealed pigment-dependent susceptibility: cinnabar was most affected, while white Kremser remained stable. Mineralogical, chemical (Cu, As), molecular (α- to β-cinnabar), and micromorphological changes (fusion of the mineral particles) were confirmed. Although binders provided slight protection, alterations primarily involved the inorganic fraction. Depending on the type of sample, an increase in frequency results in greater changes in tempera, whereas an increase in energy/pulse provokes more pronounced effects in tablet, especially in AZ and OR.