Methodologies for the characterisation and identification of atacamite in Andean colonial painting

Abstract

Painting materials used in colonial art comprised pigments and binders from European origin as well as those that were already known in pre-Hispanic times. Recently, we have identified and characterised for the first time the local mineral atacamite, a basic copper chloride (Cu2Cl(OH)3), in the polychromy of the sculpture of the Virgin of Copacabana (1582) from the Viceroyalty of Peru. This work proposes a methodology based on a multi-technical approach to identify and establish the origin of the atacamite pigment in cultural heritage objects. Optical microscopy, SEM-EDS, FTIR-ATR, micro-Raman spectroscopy, and XRD were applied to analyse mineral samples from the Andean region of Chile and Argentina as well as atacamite obtained as a secondary product in several traditional recipes used to produce verdigris, copper acetate, as viride salsum by Teófilo Presbítero (SXII). In America, between the 16th and 18th centuries, several manuals and books of secrets that described the process of making this pigment were available. One of those was the Spanish translation, commented and annotated by Andrés de Laguna in 1566, of "De Materia Médica" from Dioscorides. This methodology will be useful to establish relationships between reference samples and micro-samples extracted from colonial art objects and paintings of the 17th and 18th centuries. At the same time, it will give us information on manufacturing processes and sources of supply of atacamite. These studies will contribute to the history of colonial art and to the knowledge on technological capacities in the Andean region during this period.