Assessing Mexican pottery paint recipes using particle-induced X-ray emission

Abstract

Decorated pottery dating from the Epiclassic through Early Postclassic (ca. A.D. 650-1150) was selected for chemical characterisation of pottery slips and paints. Specimens include pottery types commonly occurring across the Basin of Mexico and Tula, Hidalgo. Recipes for slips and paints require training and first-hand knowledge of specialised techniques in production. A high degree of similarity of recipes across the region suggests widespread knowledge in the preparation and use of paint and slip. Distinct patterns in rare elements suggest differentiation in locally available pigments, and clays reflect regionally available sources of materials and differences in recipes. Particleinduced X-ray emission (PIXE) is a nondestructive method of identifying concentrations (in ppm) for 18 chemical elements. Data collection was conducted by the author using the Arizona State University (ASU) ion beam analysis of materials (IBeAM) laboratory. A sample of 136 pottery sherds was chosen and PIXE was conducted on red, black, white paints and slips. Specimens were chosen from a larger sample previously assessed for compositional characterisation of ceramic paste using instrumental neutron activation analysis (INAA). Results indicate that variation in red paints are high in iron-oxide and vary by pottery type. Black paint in Aztec I pottery is high in iron (Fe) and manganese (Mn), indicating a Fe-Mn paint recipe. Cream coloured slips vary by region and pottery type. PIXE characterisation identifies the chemical element concentrations contributing to the colourant pigments, the clay matrix in the binding materials, and trace indicators of localised impurities in clays and minerals contributing to paints and slips.