Archaeometric study of a set of ceramic materials from the old earthenware factory of Sargadelos (Lugo)

A recent preventive archaeological intervention in a landfill site of the old earthenware factory of Sargadelos has allowed the recovery of an important set of ceramic materials composed of glazed and unglazed earthenware, decorated and non-decorated, mainly from the second half of the 19th century. The goals of the research consisted in studying the microstructural characteristics of the ceramic body and the decorations, in determining the crystalline phases and establishing the possible firing temperature of the different materials, in determining their chemical composition, as well as in identifying the chemical species responsible for the coloring of decorations. The research was undertaken by conventional techniques such as binocular magnifying glass, petrographic observation by thin-section, X-ray diffraction, X-ray fluorescence spectrometry, field emission scanning electron microscopy with energy dispersive X-ray microanalysis and visible spectrophotometry, on a selection of 40 ceramic fragments. Hand-made, stamping, and airbrushing decorations were identified. The results indicated that earthenware was made from a homogeneous mixture of kaolin, quartz and feldspar; and fired approximately between 1000-1100°C. Lead-alkaline-earth type glazes in which SnO2 was sometimes detected as opacifier were identified. The chromophores of the decorations were Co2+-ions for blue, Mn3+-ions for pink, Cr3+-ions for green and the conjunction of Ni2+/Co2+/Cu2+-ions for black.