Raman study of Yuan Qinghua porcelain: the highlighting of dendritic CoFe 2 O 4 crystals in blue decorations
Résumé
Raman spectroscopy and scanning electron microscopy equipped with energy dispersive spectrometer (SEM-EDS) were used to analyze the decors of the Yuan blue and white porcelains (Qinghua porcelains). SEM-EDS carried out on the dark spots of the blue decors revealed the presence of dendritic crystals of a mix cobalt iron oxide. The Raman spectra of these crystals are close to the standard spectrum of cobalt ferrite (CoFe 2 O 4). Comparing the Fe/Co ratios obtained by EDS to the corresponding Raman spectra, we have identified two main types of spinel crystals: one type richer in iron and another type richer in cobalt. Both types of spinel cause the blackening of the blue decors. It is the first time that spinel crystals with a composition close to cobalt ferrite were observed as the main constituent of the dark spots in blue decors of Qinghua porcelains.