Nd:YAG long Q-switched versus short free-running laser cleaning trials at Chartres cathedral, France

Laser cleaning trials using Nd:YAG (1064 nm) devices on outdoor sculptures at Chartres Cathedral, France, revealed that short free-running (SFR) mode at 300 mJ output energy and long Q-switched (LQS) mode at 150 mJ output energy effectively preserved the oxalate layer lining the stone surface while removing black crust. The LQS mode resulted in a slightly yellowed appearance, whereas the SFR mode produced a darker but less yellow surface. Microscopic and scanning electron microscope analyses confirmed that both laser regimes maintained the oxalate layer, with minimal trace of black crust remaining under the chosen operating conditions. These findings suggest that precise control over laser parameters can optimize cleaning efficacy while safeguarding the stone's structural integrity.

Vergès-Belmin, V., Rolland, O., Jourd’heuil, I., Guiavarc’h, M., & Zanini, A. (2015). Nd:YAG long Q-switched versus short free-running laser cleaning trials at Chartres cathedral, France. Studies in Conservation, 60(sup1), S12–S18. https://doi.org/10.1179/0039363015z.000000000202