Technological and compositional study of the gold leaf from Baroque altarpieces – basis for a research methodology

Abstract

The gold leaf from one of the most important art works of the Portuguese Baroque period, the main altarpiece of the Church of Jesus in Aveiro, currently part of the city Museum and former Convent of Jesus, was studied. Qualitative analysis of the samples cross-section was performed by optical microscopy. Three different layers – ground layer, bole and gold – were identified, a result consistent with a traditional gilding. The use of scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) showed the use of a ternary Au-Ag-Cu alloy, with approximately 22 carats. Through inductively coupled plasma mass spectrometry (ICP-MS) it was possible to identify trace elements such as Cr, Pt, Pd and Sn in the gold, and Pb and Hg in the bole layer. The use of synchrotron radiation micro X-ray fluorescence (SR-µXRF) confirmed the presence of Sn and allowed to establish a profile of the main elements in the samples.