Technology of Maltese Baroque oil-based wall paintings

The technology of Baroque oil-based wall paintings in Malta: Materials and implications for conservation (PhD research: Roberta De Angelis – completion date 2021)

This research aims to gain a holistic overview on the materials and technique of oil painting on stone in Malta in the Baroque period (17th and 18th c.) and to assess its inherent susceptibility to degrade.

Art historical sources describe the Baroque period in Malta as an animated cosmopolitan artistic environment that coexisted with a more vernacular component (Sciberras 2012). In this context, oil painting on walls became a popular technique, employed by local but also foreign artists primarily from southern Europe working on the Island, and remained as such until the 20th c. (Buhagiar 2006). The peculiarity of this technique lies in its painting system in which oil paints are applied directly to a very porous limestone substrate usually without the interposition of lime plaster.

Although this research topic has important art historical ties, it is the implication of this specific technology on conservation that is at the core of this research. Oil paints are, in fact, recognised as being reactive chemical systems that respond to environmental factors. This often generates visual and other physical changes that have a strong influence on the conservation strategy and treatment options for these paintings. Not understanding fully these effects can seriously compromise a conservation treatment, as well as the work of art itself. An overwhelming amount of research has been carried out on easel paintings from museums to understand these changes and degradation processes over the last 25 years, whereas wall paintings clearly lag behind.

Technology and degradation are strongly interconnected in oil painting, and it is not possible to gain a good understanding of the technology of oil paintings without being aware of the changes caused by their chemical instability (Stols-Witlox 2017; Spring and Higgitt 2006). For this reason both composition and degradation of the stone-oil systems are a major focus in this research.

The research methodology is strongly based on local case studies. Seven case studies have been selected, including paintings from local artists, such as Alessio Erardi and Enrico Regnaud, as well as foreign artists, such as Mattia Preti. The analytical protocol followed largely reflects commonly used methods in the field, including, when possible, in situ non-invasive examination techniques, followed by micro-sampling and invasive laboratory techniques. These include optical microscopy, scanning electron microscopy (SEM) coupled with energy dispersive X-Ray analysis (EDS), Fourier transform infra-red (FT-IR) and Raman spectroscopy, and gas chromatography coupled with mass spectrometry (GC-MS). More sophisticated techniques, such as Synchrotron Radiation-based micro X-Ray diffraction (µXRD), micro X-Ray Fluorescence (µXRF) are also being considered to characterise specific degradation products, along with X-Ray absorption near edge structure (µXANES).

Prof. JoAnn Cassar, Professor, Department of Conservation and Built Heritage (University of Malta)
Dr Austin Nevin, Senior Lecturer (University of Gothenburg)