Art Diagnosis Centre

Holy icons created in the Byzantine era are a vital entity in Orthodox Christianity, a living tradition unbroken over more than 1500 years. The importance of these symbolic representations has inspired interdisciplinary studies to better understand the materials and process of their construction. Researchers from a variety of fields are working together to place icons in their proper historical and cultural framework, as well as to develop long-term conservation strategies. In this Account, we review very recent analytical results of the materials and painting methods used in the production of Byzantine iconography.
The care of icons requires particular attention because of their function; icons are objects of veneration and, for the most part, still stand in today’s churches to serve ritual practices. Accordingly, they are affected by random, fluctuating environmental conditions aggravated by public access. Because of the holiness of the icons, the typical tradition of the church is to periodically restore the depicted scenes, either by retouching any defects or by partial or complete overpainting. These interventions greatly increase the complexity of the paint stratigraphy. To reveal the extent and quality of the original painting under several historical overpaintings or dirt overlays on the icon, researchers usually pursue a manifold approach, combining complementary multispectral imaging and spectroscopic techniques nondestructively.
Unfortunately, a visual and exhaustive spectroscopic examination of a minimum number of cross-sectional microsamples is almost always necessary to clarify the structure of the paint layers and map the constituent materials identified therein. A full understanding of these details is critical for assessing the painting methods, stylistic conventions, and compositional concepts that render the different iconographic details. Cross-sectional micro-Raman spectroscopy, although time-consuming, now affords the direct identification of the distinct grains of almost all of the inorganic pigments and inert components included in the paint layers. Micro-Raman studies are complemented and cross-checked by micro-FTIR and scanning electron microscopy−energy dispersive spectroscopy (SEM−EDS) studies. This approach is essential in documenting the evolution of the materials and techniques used in creating icons over the centuries.
Analytical data on Greek icons are now available for comparison with similar results from other important schools of iconography, such as in the eastern Mediterranean, the Balkans, or Russia, or, further, with Western schools of painting. The research constitutes a reference base for identifying and solving analytical problems, such as those related to the organic materials found in icons that have not yet been systematically studied. Moreover, the results on icons are also generally applicable to important analytical issues encountered in studying any multilayered paint stratigraphies.

The St. Euthymius wall paintings, in the Cathedral of Thessaloniki, dated 1303 AD., are stylistically attributed to the School of Panselinos, one of the most important painters of Palaeologean Art.
An in situ non-invasive study has been carried out as part of a MOLAB project (a mobile laboratory accessible through the Eu-ARTECH project, funded by the EC 6th FP) combining different analytical techniques such as XRF, mid-FTIR and UV-vis diffuse reflectance spectroscopy. It was during this comprehensive in situ study that certain scientific queries were raised about sensitive areas, where indications of the phenomena of decay requested further attention. A subsequent laboratory study of selected cross-sections using microscopic analysis with μFTIR, SEM-EDS and μRaman, further confirmed the identification of only the atypical in situ observations.
The comparative interpretation of all respective results on the specific regions of interest permitted the identification of several degradation phenomena which justify certain aesthetic or stylistic incoherences in the representations. Namely, (i) thermal dehydration of the yellow ochre explaining the reddish appearance of the flesh tones and halos as an accidental effect of the fire; (ii) thermal degradation of azurite converted to tenorite explaining the atypical instance of dark lightings on the purple garments; (iii) degradation of red lead employed in the lightings of the red garments; (iv) widespread presence of oxalates in the paint surface.

What the discerning gaze of the art historian has deduced from comparisons in style – namely, that the unsigned Baptism of Christ (dated 1567) comes from the hand of the master Cretan painter, El Greco – is now investigated by the dispassionate eye of technology. The examination by means of analytical methods of diagnosis aimed at making an in-depth investigation into the hitherto unknown personal traits of the artist’s painting technique. By observing the cross-sections under the optical microscope and analyzing the materials through the application of μRaman and μFTIR spectroscopies and of high performance liquid chromatography (HPCL/DAD), it was possible to reveal the “fingerprints” of the artist’s brushwork.
In his masterfully executed Baptism, El Greco has succeeded through his perspicacity and ingenuity, to combine traditional techniques of Byzantine icon-painting with the innovative practices of Venetian Renaissance art. The artist’s palette contains mineral, earth and natural organic pigments, as well as some synthetic ones of glass or resin base: lapis lazuli, indigo, lead-tin yellow, orpiment, yellow ochre, cochineal lake, copper resinate, burnt umber, lead white and carbon black. Furthermore, he introduces a layer of white imprimatura containing varied combinations of powdered glass and lead white. The detection of substantial similarities between the glass varieties used in the Baptism and those found in works by Venetian painters contemporary with El Greco (such as Tintoretto) further attests ascription of the Baptism to the period of the artist’s brief sojourn in Venice.

According to the archaeological deductions, the origin of true purple dyeing technology is proven native
of the Aegean world, dating at least from the 1700 - 1600 B.C., including indications of earlier developments
belonging to Neolithic levels. Although the continuing fame of purple is always related to the prestigious
garments of royalty or to high ranks of society and religion, archaeological evidence of any early dyed
textile preserved is extremely unlikely to come to light, because of the fragility of the fibre substrate. The
identification of the conchylian purple dyestuff in the form of a pigment, found applied on the wall
paintings at Akrotiri of Thera, is shown to be of equal importance as being the earliest tangible evidence in
the Aegean for the development of the vat dyeing technology in the early Late Bronze Age.

"The purpose of the present research was to compare the effect of different embedding and polishing procedures on the performances achievable with Fourier Transformed Infrared (FTIR) microscopy in Attenuated Total Reflection (ATR) mode. The attention was specifically focused on this technique since it is generally
considered one of the most appropriate methods to analyze cross sections, thanks to the fact that the recorded spectra are similar to those collected in transmission mode.
The research work was structured as a round robin among six different conservation and research laboratories.
They were asked to embed fragments derived from the same area of a real sample following each one a different procedure. The performances of FTIR microscopy in ATR mode were evaluated on the different cross sections, considering the cross section morphology and the possible source of contamination. The cross sections were previously observed with optical microscopy, Environmental Scanning Electron Microscope
(ESEM) and confocal microscopy.
Three procedures were eventually selected, because they provided the best results in terms of both limiting the contamination of the embedding medium and achieving good contact with the ATR crystal. They were: a) embedding in KBr; b) cyclododecane pre-treatment before embedding in an organic resin and cutting of the sample; c) embedding in an organic resin and polishing with argon ion milling.
These three procedures were finally compared and the weak points outlined, indicating where improvements could be made for further researches."