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Ultramarine has been for centuries one of the most highly prized pigments of all traditional artists’ materials, due to its durability, excellent color, and its intrinsic value. For the production of the blue pigment Ultramarine, the rare semiprecious stone Lapis Lazuli has been used, found since ancient times in mines northeast of Afghanistan, making it difficult to transport to the Mediterranean region. Since 1828, when the synthetic form was discovered, it has become widely used and synthetic Ultramarine blue has replaced the natural variety in painting palettes. Therefore, one key objective in authentication issues is to distinguish between natural and synthetic Ultramarine. In this research work, ten commercial Ultramarine pigments -of both natural and synthetic origin- were used to investigate the possibility of their discrimination using various characterization methods. The pigments were studied by Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry (XRD), electron microscopy (SEM-EDS), and UV-Vis spectrophotometry. The combination of elemental composition, morphological analysis, phase identification, color calculation, and optical band gap estimation is used, towards an analytical protocol for the discrimination between samples of synthetic and natural origin.
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Pourliaka et al. (2023) studied this question.