Nevers City Earthenware Blue Glaze: pXRF Categorization from Cobalt Sources and Raw Materials Impurities: Comparison of Reasoned and Chemometrics Methods

The blue, white, and black glazed areas of nineteen Nevers earthenware pieces bearing a date or precisely datable between 1589 and 1865 were for the first time analyzed by X-ray fluorescence spectroscopy at the Musée de la faïence et des Beaux-Arts-‘Frédéric Blandin’ in the city of Nevers by pXRF in order to categorize the raw materials and recipes used. The semi-quantitative signal comparison of major elements and impurities such as rubidium, strontium and zirconium shows the use of the same raw materials except for six artifacts. At least three types of cobalt, characterized by association with copper, nickel, and manganese, are observed. Different blacks (with manganese or bismuth) are observed. A comparison is made between the classification obtained with chemometry (z-score, PCA, and dendrograms of similarity) and a reasoned analysis of ternary diagrams based on the signal of the most characteristic elements. This preliminary work demonstrates the potential provided for the categorization of enameled ceramics and their dating through non-invasive on-site semi-quantitative elemental analyses. No important advantages were observed for the chemometric procedure: the same conclusions are obtained by quantitative comparisons of the XRF data, but the chemometric procedures allow a clear visualization of the main conclusions.