HISTORICAL SYNTHESIS AND POTENTIAL DEGRADATION OF YELLOW AND RED CADMIUM PIGMENTS

HISTORICAL SYNTHESIS AND POTENTIAL DEGRADATION OF YELLOW AND RED CADMIUM PIGMENTS Elena Castagnotto, Giacomo Baldasso, Pamela Isola, Marta Campolucci, Pietro Manfrinetti, Maurizio Ferretti, Stefano Alberti, Federico Locardi Dipartimento di Chimica e Chimica Industriale, Via Dodecaneso 31, 16146 Genova - Italy Cd-based pigments were introduced in the 19th century and revolutionized the colour palette of artists. The primary component is the orange CdS, with ternary compounds fabricated later to achieve adjustable hues [1,2]. Adding Zn, the colour tunes to yellow increasing the Zn amount, whereas red pigments can be obtained by substituting sulfur with selenium. Extensive research has demonstrated how Cd-based pigments are characterized by a high level of heterogeneity in terms of colour, presence of impurities, coexisting of different phases, and particle size. This heterogeneity is induced by the variability of the synthetic methods employed by the different companies, with direct influence of the long-term stability of these materials. Indeed, the lack of precise information of the composition of the pigments obtained following the historical syntheses limits the prediction of the possible deterioration in real paintings [3]. In this study, we synthesized a series of CdxZn1-xS and CdS1-xSex pigments following established historical formulations. The synthesized pigments exhibit similar hues but vary in crystalline structure, particle morphology, and size. Additionally, different secondary phases are identified. The materials underwent artificial aging under simulated solar illumination to assess potential degradation. Subsequently, photocatalytic tests were conducted to correlate the observed alterations with their intrinsic semiconductor properties. The results revealed important information about the deterioration behavior of historical pigments, identifying key indicators of pigment reactivity in real artworks and demonstrating the inherent instability of historically synthesized pigments based on fabrication methods. [1] I Fiedler, Bayard, M. Artist’s Pigments - A Handbook of Their History and Characteristics; Feller, R., Ed.; National Gallery of Art: Washington, 1986. [2] Dunning, P. Cadmium Pigments. High Perform. Pigment. Second Ed. 2009, 13–26. [3] E. Castagnotto et al. Chem. Mat. (2025) accepted manuscript