Scientific Essay from the year 2003 in the subject Engineering - Civil Engineering, , course: EUROMAT 2003, language: English, abstract: Laser cleaning of polychrome surfaces is currently problematic due to the fact, that laser irradiation can cause damage of the paint layers. A test program was worked out to analyse the chemical and physical background of these typical pigment blackening effects. The analytical methods ESEM, XRD, DTA, FTIR and NMR were used to describe the reactions of inorganic pigments and organic binding media caused by laser irradiation. The used laser system is commercially available, is currently used for the cleaning of natural stone surfaces and works at a wavelength of 1064 nm. The discoloration of pigments and paint layers was documented by colour measurement. Further the measurement of discoloration thresholds of energy density (of pigments and paint layers) was a main part of the research.