In optical coating production the generation of particles and defects is always an undesirable side effect and cannot be completely avoided in the handling steps of the optical components. Particles and defects on the substrates and in the functional coatings lead to scattering and absorption, which may cause a lower damage threshold for components of high power laser application. In this study, results of a long term investigation in the quality and the state of the cleanliness of multilayer systems produced by different deposition techniques are presented. Coated samples of different coating processes are investigated with the help of a Fast Total Scatter scanning system. Adapted data reduction algorithms for the determination of the particle sizes derived from the scattering measurements are developed and applied to the measurement results. On this basis, the density distribution of particle contamination on the samples is evaluated for selected coating runs over a long term period. The calculated statistics of the samples are related to the corresponding production conditions of individual coating plants to extract specific effects of the process environment.