By comparing the chemical composition, the crystalline structure, the size and the appearance of the particles, it is possible to identify the pigments of a sample. Furthermore, the identification of synthetic organic pigments and dyes of the 20 th century is of great importance for authentification. Primarily thin layer chromatography is currently used for this purpose. A spectral photometer is available for colourimetry and for recording reflectance curves in the visible part of the spectrum. The photometer can follow changes in colour, for example, over longer periods in the paintings themselves or in test samples.