Medium-wave ultraviolet radiation to eliminate laser-induced yellowing generated by the laser removal of lamp black on gypsum

International audienceExperiments were conducted to evaluate the impact of UV-B exposure on yellowing induced by Nd:YAG Q-switched laser cleaning (1064 nm) on gypsum samples previously soiled with mixtures based on lamp black and gypsum. Colour measurements were carried out to monitor and characterize samples, thus enabling quantification of the yellowing effect due to laser cleaning and monitoring of the reverse whitening effect due to UV-B exposure. The dose–response function to UV-B was calculated as a function of increasing exposure time to UV-B; it depends on the composition of the soiling mixture. These experiments show that the components of lamp black, mainly carbon, are involved in the yellowing effect induced by laser cleaning. They also indicate that UV-B exposure is able to mitigate this effect considerably