Application limits of Q-switched Nd:YAG laser irradiation for stone cleaning based on colour measurements R.M Esbert, C.M Grossi, A Rojo, F.J Alonso, M Montoto, J Ordaz, M.C Pérez de Andrés, C Escudero, M. Barrera, E Sebastián, C Rodríguez-Navarro, K Elert • 2003