Luminescent Inorganic Pigments Used in Ancient and Modern Times

Most inorganic pigments, as earths and ochres, have no luminescence emission. Sporadically, the literature has reported the presence of a weak optical emission for some of these pigments. However, this should be attributed to the presence of material impurities within pigments. In addition to this, a small number of inorganic pigments exhibit a clear luminescent emission, which can be used to identify them and study their behavior from a conservation point of view. These are primarily modern pigments, used in modern and contemporary art, and a few pigments used since ancient times. In this chapter, we provide a non-exhaustive list of them. Section 1 describes the luminescent emission of the ancient pigment lead white. Section 2 discusses the luminescent characteristics of zinc white, the principal white pigment of the modern age. In Sect. 3, the luminescent characteristics of titanium white are illustrated. Finally, Sect. 4 describes the luminescent properties of cadmium-based pigments. The list of inorganic luminescent pigments should be completed with the case of Egyptian blue, considered as the first synthetic blue pigment, produced in Egypt around 5,000 years ago and since then widely used in the Mediterranean area until the end of the Roman period and beyond. Egyptian blue displays an exceptionally high near-infrared photoluminescence emission, peaked around 910 nm and with a lifetime of about 107μs. The emission, easily stimulated by visible light (typically with green or red light) can be used to identify the pigment and its spatial distribution on the surface of artworks and archeological artifacts even with the use of a simple digital camera with the infrared barrier filter removed. Finally, barium white and calcium carbonate can display an optical emission ascribed to metal substitutional ions in the crystal matrix of the materials. Nonetheless, up to now, the full comprehension of the optical emission of these two materials is relatively scarce.