The synthesis and quality comparison of nineteenth-century chromate pigments: strontium, barium, zinc and cadmium chrome yellow

Abstract This study presents a detailed comparison of the yellow chromate pigments strontium yellow SrCrO 4 , barium yellow BaCrO 4 , zinc yellow KZn 2 (CrO 4 ) 2 ·H 2 O(OH) and the rare cadmium chrome yellow 2CdCrO 4 ·KOH·H 2 O, to allow their identification in fine art. Historical recipes from the late nineteenth century were used to synthesise these pigments to ensure they were prepared in an authentic manner. The characteristics of the pigments were established through X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The colour properties of the pigments and pigment-oil systems were evaluated using the CIE L*a*b* system. Zinc and cadmium chrome yellows showed the highest chroma and yellow contribution, while strontium yellow exhibited a significant degree of green hue and the lowest amount of yellow hue. The light stability of the chromate pigments tested is influenced by their elemental composition, method of synthesis and the surrounding medium. Graphical abstract