ColoRaman project

An on-line database has been compiled providing the Raman and fluorescence spectra, obtained using three different excitation wavelengths (531.5, 632.8, 780 nm) of 99 pigments analysed dry and already applied with four painting technique (egg tempera, casein tempera, oil and fresco). The database makes it possible to easily determine the most suitable excitation wavelength for the identification of  pigments already applied with these painting technique. The binding agents and ground material, almost always of organic origin, are responsible for a fluorescence which in many cases is so intense that it covers the weak Raman signal emitted by the pigment, making it impossible to identify the latter. In many cases, however, it is possible to improve the signal-noise ratio (noise here consisting of the emission of fluorescence) by adopting an appropriate excitation wavelength. This wavelength will depend on the pigment and on the painting technique used because the different materials employed to produce binding agents and grounds can contribute in different ways to mask the Raman signal.The pigments were used in the laboratory according to documented recipes . It was then possible to perform measurements on a specimen produced using specifically selected materials and techniques. See recipes and products for the four painting techniques in the “Painting” site section.