Naturwissenschaften und Technologie in der Kunst; Akademie der bildenden Künste Wien; Schillerplatz 3; 1010 Wien
Research > Projects > Material Analysis > Historical Pigments Print

Pigment Analysis by Means of the Micro-Raman Spectroscopy – Extension of the Existing FTIR, XRF, and XRD Database by the Raman Spectra

Raman spectra of approx. 200 white, yellow, orange, brownish and red inorganic pigments have been collected. The investigations were performed using the confocal LabRAM ARAMIS Vis spectrometer (Horiba Jobin Ivon) equipped with 3 lasers (785 nm, 532 nm, and 632.8 nm).

Before the Raman library is built up, the spectra are evaluated in the following way: first, the results of the Raman measurements were compared with the information gained by previous XRF, FTIR, and XRD measurements. In a second step, a Raman data base is built up using the most representative spectra of each pigment sample. All spectra are base line corrected in order to remove the fluorescence background. In the case of pigment mixtures, as found in many pigment samples, the Raman spectra show different bands depending on measured pigment grains and the laser used for the measurement. This means that more than one spectrum containing different compounds were considered for the Raman database for the pigment with the same inventory number.

Compared to FTIR spectroscopy, high lateral resolution which can be achieved in Raman spectroscopy allows the non-destructive analysis of the particles down to 1 µm lateral resolution. Thus, very precise measurements can be performed on pigment grains of different colours and shapes which give spectra without overlapping bands of two or more components in the sample. According to this the identification of different components (fillers, pigments etc.) contained in one sample can be performed easily.

Furthermore, several inorganic pigments widely used in paintings (e.g. cinnabar, cadmium yellow, zinc oxide, realgar, massicot/litharge etc.) don’t show IR spectra in the mid IR range, but they can be clearly identified due to their Raman spectra. Also identification of inorganic, carbon based black pigments (e.g. charcoal, lamp black) can be easily carried out by means of Raman spectroscopy.