The impact of laser radiation on fresh and soiled sandstone: Application to the cleaning of monuments and buildings

摘要

The use of a Q-switched Nd:YAG laser as a rapid non-contact method for removing soiling layers form sandstone is reported. Colour measurements of unsoiled stone were made using a Minolta Chroma meter to provide target values for the laser treatment. Colour measurements and examination using optical and electron microscopy of the fresh and soiled stone prior to and after laser treatment showed that 1064nm laser pulses were efficient at removing the polluted layer and at retaining the original colour of the stone. The optimum laser pulse energy was found to be 4.88mJ, above which damage to the stone surface occurred, resulting in a bleaching of the stone.