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