Investigation of the Cross-Section Stratifications of Icons Using Micro-Raman and Micro-Fourier Transform Infrared (FT-IR) Spectroscopy

Abstract

The cross-section stratifications of samples, which were removed from six icons, are studied using optical microscopy, micro-Raman spectroscopy, and micro-Fourier transform infrared (FT-IR) spectroscopy. The icons, dated from the 14th to 19th centuries, are prominent examples of Byzantine painting art and are attributed to different artistic workshops of ​​northern Greece. The following materials are identified in the cross-sections of the icon samples using micro-Raman spectroscopy: anhydrite; calcite; carbon black; chrome yellow; cinnabar; gypsum; lead white; minium; orpiment; Prussian blue; red ochre; yellow ochre; and a paint of organic origin which can be either indigo ( Indigofera tinctoria L. and others) or woad ( Isatis tinctoria L.). The same samples are investigated using micro-FT-IR which leads to the following identifications: calcite; calcium oxalates; chrome yellow; gypsum; kaolinite; lead carboxylates; lead sulfate (or quartz); lead white; oil; protein; Prussian blue; saponified oil; shellac; silica; and tree resin. The study of the cross-sections of the icon samples reveals the combinations of the aforementioned inorganic and organic materials. Although the icons span over a long period of six centuries, the same stratification comprising gypsum ground layer, paint layers prepared by modified "egg tempera" techniques (proteinaceous materials mixed with oil and resins), and varnish layer is revealed in the investigated samples. Moreover, the presence of three layers of varnishes, one at the top and other two as intermediate layers, in the cross-section analysis of a sample from Virgin and Child provide evidence of later interventions.

Unveiling the original layers and color palette of 18th century overpainted Transylvanian icons by combined X‐ray radiography, hyperspectral imaging, and spectroscopic spot analysis

“…The strong absorptions around 2,920 and 2,850 cm −1 (C─H stretching vibrations), along with the strong peak at 1708 cm −1 indicate the use of a natural resin (Figure 12), applied as a varnish layer. [ 9 ] The intense C─H absorptions in the upper part of the spectra fall in position similar to those of oil, suggesting the possibility that a lipid binder may also be present. This hypothesis is sustained by the carbonyl peak observed around 1730–1738 cm −1 and the peaks observed at 1164 and 720 cm −1 (Figure 9), these last ones ascribed to fatty acids present in oils.…”

“…The use of anhydrite within the ground layer is not uncommon, [ 9 ] previous studies carried on Transylvanian icons showing a preference for calcium sulfate‐based grounds. [ 13–15 ] As shown in other studies, [ 9,20 ] various proportions of gypsum and anhydrite can be found within the ground layer, the high concentration of anhydrite being most probably linked with a poor lack of control of the calcination process of gypsum. [ 27,28 ]…”

“…Most probably, for the red hues, a mix of red ochre and red lead was used, [ 31 ] while for the orange hues a mixture of red lead with a yellow based pigment was preferred. [ 39 ] Cinnabar/vermillion (HgS), a widely used pigment in Byzantine iconography, [ 9 ] can be ruled out as no Hg lines were registered within the XRF spectra.…”

“…[ 37 ] However, FTIR spectra registered on these same green areas did not show any of the characteristic absorptions of chromium(III) oxide—main peaks at 632 and 566 cm −1 due to various combinations of O 2− and chromium (III) displacement in the lattice. [ 41 ] Instead, characteristic signatures for barium chromate (doublet at 846 and 834 cm −1 ) [ 39 ] and Prussian blue were found (diagnostic peak at 2090 cm −1 ) [ 9 ] (Figure 12). These findings suggest that, for the green hues a mixture of chrome yellow and Prussian blue was used.…”

Using SiO₂ nano-particles for better color uniformity and lumen output in 8500 K conformal and in-cup white LEDs

“…On the other hand, the chromatic uniformity in remote phosphor structure is not ideal due to the shape of the encapsulation layer is hollow at the center. This leads to the uneven density of phosphor at different angles resulting in a yellow border around the emitted light of the device [20]. To enhance the overall performance of WLEDs, we applied the SiO2 particles which have shown positive results in our experiments regarding the color temperature consistency and light output.…”