The aim of this study was to investigate the original materials and techniques used in the Roman and the Byzantine wall paintings of Caesarea. In addition, it was intended that such a study should contribute to the conservation of these paintings, since an understanding of the nature of the materials is essential for assessing their current condition and their susceptibility to future deterioration.
The recent excavations in Caesarea have revealed many interesting wall paintings, some of which are unique for the area, such as the 'Animals' scheme in the Roman hippodrome and the early Byzantine paintings with Christian iconography in the vaults complex.
The study involved an initial period of collection of archaeological and conservation documentation, and then in-situ examination of all the paintings. Based on this, thirteen of the twenty-eight schemes of painting were selected for detailed investigation and scientific analysis.
Various techniques were used for the examination and analysis, including polarised light microscopy (PLM), micro-chemical testing (MCT), scanning electron microscopy with an energy dispersive x-ray analysis (SEM-EDX), x-ray diffraction (XRD), and Fourier transform infrared microspectroscopy (FTIR).
As anticipated, there were some very interesting results. The range of pigments found was extensive, including red lake, cinnabar, malachite, and possibly ultramarine, as well as the more common pigments: calcium carbonate white, haematite, red and yellow ochre, green earth, Egyptian blue and carbon black. From this palette Caesarea's painters produced an extremely wide range of hues and tones, both by mixing and layering the various pigments. It is presumed that most of the paintings were executed in lime-based techniques, though some of the materials, such as red lake and cinnabar, would have been bound with an organic medium. Although the plasters are all lime-based, there is a particularly wide range of aggregate types, mixing ratios, and application methods, including polishing. In most instances, the aggregates were identified as local materials, typically from the shore gravel including mainly quartz sand, calcareous sandstone and bioclasts. Plasters with crushed calcite occur, and reflect the practice described by Vitruvius. Crushed ceramic material (as well as large sherds) was used, and it seems likely that the plaster for the Byzantine nymphaeum was hydraulic.
Several aspects of the original technique were observed to have a direct bearing on conservation issues: for example, the preferential deterioration of white in Roman painting; the susceptibility to erosion of plasters with large aggregates in the final plaster layer; and, quite significantly, the occurrence of pigments subject to photodeterioration such as red lake and cinnabar.