Icons: Production techniques and examination methodology
Icon or ikon from Greek eikōn is a representation of a sacred or sanctified Christian personage used in religious worship in the Russian or Greek Orthodox Church. The production of icons has been described by the monk Dionisios ek Fourna in 1728-1733. Icons are typically painted on a wooden panel with the egg tempera painting technique, over a layer of gypsum and glue (preparation layer). Sometimes, canvas is present between the wood and the preparation layer. The painter with the aid of a sharp tool or with diluted tempera colour either incised or paint the preparatory drawing. Afterwards the golden leafs were attached using the bolo technique. The brush work initiates with a brownish colour (proplasmos), over which softer tones were applied (sarcoma) darker for shadows or lighter and reddish for highlights. The last step is the varnishing of the icon.
The use of diagnostic methods and the extensive examination of the painting surface is an inseparable part of research, condition assessment and proper justification of the artwork. Icons diagnostics contribute in documentation and recording, as well as in the understanding of deterioration factors and evaluating the present condition, including the materials and techniques used by artists and past restorations.
Potential of RTI in icons
The application of RTI in icons is prosperous area of research because icons are artworks of great historical and artistic value, well distributed around the world, which present interesting surface topography, difficult to capture and examine using conventional methods, due to their planar shape and their reduced three-dimensional characteristics, along with the gold or silver gilded areas. Moreover, icons layering structure as well as the interesting colour palette used by artists can lead RTI technology to methodological developments. Notable is also that RTI can be an excellent addition to the icons examination protocol, which has been the matter of thorough research, either destructively, using analytical methods (Raman spectroscopy, SEM-EDX, GC-MS) or preferably non-destructively (optical microscopy, multi-spectral imaging, X-radiography, computer aided tomography, XRF).
Nevertheless icons consist of an artefact type, which has received minimum attention, regarding RTI applications. Zányi et al. underlined the inefficiency of photography or active 3D range scanning in capturing gold, silver leafs and tempera painting technique of icons. Their case study, of the apse mosaic at the Angeloktisti Church at Kiti, Cyprus, highlighted the efficiency of RTI in capturing gold, silver and glass tesserae, providing an advanced perception and enabling explorations of the various different views of the mosaic (Zányi, Schroer, Mudge, & Chalmers, 2007).
In this case study the icons are modern replicas, painted using the traditional materials and techniques of byzantine egg-tempera painting, representing St John, St Proxoros and Jesus Christ (Figure 1).
RTI results and discussion
RTI visualization of icons emphasizes surface anomalies of low relief details. Characteristic features, such as brush strokes can be detected and painting techniques can be investigated. Thorough RTI examination of the surface topography reveals signs, which provide an insight into manufacture, such as gold gilding technique. Moreover, assists in condition reporting, because areas with discontinuities can be easily documented (Figures 2 and 3). Hence, RTI can be extremely useful for diagnostic examination.
The IR-RTI of the paintings, taking into consideration their planar shape and their reduced three-dimensional characteristics, gave interesting results, revealing hidden features and the preparatory drawing. IR-RTI by penetrating the varnish layer, the texture of the substrate can be observed. RTI reveals the texture of the varnish applied while in the IR-RTI renderings the texture of the substrate is visible, along with its deformations, such as the vertical crack on the area of the basket. The preparatory lines along with their texture can be examined. Final brushing of details disappear emphasizing on the three dimensional properties of the preparatory drawing. Areas where the colours have not been applied uniformly due to surface variation of the substrate become obvious (Figures 4 and 5).
Zányi, E., Schroer, C., Mudge, M., & Chalmers, A. (2007). Lighting and byzantine glass tesserae. In Proceedings of the 2007 EVA London conference.