From Ore to Pigment: A Description of the Minerals and an Experimental Study of Cobalt Ore Processing from the Kāshān Mine, Iran

Ore samples collected from the cobalt mine of Qamsar, Kāshān, were studied using optical microscopy (OM), qualitative X‐ray diffraction analysis (XRD), semi‐quantitative X‐ray fluorescence spectrometry (XRF) and quantitative electron micro‐probe with wavelength‐dispersive spectrometry (EMP–WDS). These analytical data provide the characteristics of the Kāshān cobalt ore, which can be compared with the composition of the blue pigments and colourants applied to glass and glazes, not least those of Islamic and Chinese blue‐and‐white wares. Preliminary replication studies of the pigment were also conducted according to the descriptions given in the Persian and European historical texts reviewed in a previous paper. The resulting phases were examined under an optical microscope and a semi‐quantitative energy‐dispersive spectrometer (EDS) attached to a scanning electron microscope (SEM). The ore was shown to contain high Fe and As concentrations and negligible Zn and Ni concentrations. Cobaltite (CoAsS) and erythrite (Co3(AsO4)2.8H2O) made up the two main cobalt‐bearing minerals in the ore. The washing processes that were conducted based on a historical text rendered the ore more enriched with erythrite. In light of the new data on the Kāshān cobalt ore, the origins of the blue pigments used in some of the Islamic and Chinese ceramics are reconsidered