Analytical study of polychromy on exterior sculpted stone

A complete study on the remnants of the polychromy in the main entrance portal of Saint Paul's church (16th century, Ubeda, Spain) has been carried out using Raman microspectroscopy in combination with optical microscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). The polychromy in red areas showed the superposition of two well-defined pictorial layers. The first one (probably original) was composed of cinnabar, red lead and hematite over a preparation coating containing calcite, gypsum and lead white. The second red pictorial layer was mainly constituted by cinnabar and was over a thicker preparation coating. Green samples showed a single pictorial layer over the weathered stone. The high fluorescence background made the examination of the latter samples extremely difficult by means of Raman microspectroscopy. SEM-EDX detected abundance of copper and chlorine, and a detailed inspection of Raman spectra revealed the presence of a copper hydroxychloride, analogous to the naturally occurring mineral atacamite. Azurite remnants of the original polychromy were only found in the cracks of mortar joints. Alteration products like calcium and copper oxalates were also widely distributed in this layer. Copyright (C) 2009 John Wiley & Sons, Ltd.