Naturwissenschaften und Technologie in der Kunst; Akademie der bildenden Künste Wien; Schillerplatz 3; 1010 Wien
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An Approach of Multianalytical Techniques for Studying Ultramarine Pigments

A detailed comparative analysis of eleven different synthetic ultramarine pigments, shown in Fig. 1, has been performed using x-ray fluorescence, x-ray diffractometry, Raman and infrared spectroscopy as well as colorimetry. It has been shown that only the combination of all these methods enables to gather enough information for full differentiation of the samples, and to obtain the complete characterization of each pigment.

Fig. 1: Examined powder ultramarine pigments in their original glass tubes
and support are part of the wide pigment collection consisting of
more than 1300 organic and inorganic pigments.

Although all eleven analyzed pigments were synthetic, the methods have shown that all of them beside pure synthetic ultramarine, contain other elements and other colorants as well. Therefore, the purity vs. variety and complexity of compounds and elements found in examined pigment should not be taken as an important criterion to differentiate synthetic from natural ultramarine pigments (Table 1).

Fig. 2: Concentration of S2- (relative to the concentration of S3-) plotted versus the colorimetric parameter h*, for the various ultramarine pigments investigated.

Fig. 3: Raman spectrum of the pigment no. 1273, where a TiO2 peak at 145 cm-1 is clearly visible. The S3- and S2- peaks at 550 and 585 cm-1, respectively, and peaks at 264, 818, 1100, and 1370 cm-1 identified as ultramarine peaks are shown as well.
Fig. 4: Saturation C* of the various ultramarine pigments versus their colorimetric parameter h*.