Yannis Chryssoulakis

Ochre-differentiation through micro-Raman and micro-FTIR spectroscopies: application on wall paintings at Meteora and Mount Athos, Greece

The most widely-used inorganic pigments of Byzantine and post-Byzantine hagiography are earth pigments called ochres such as, red and yellow ochres, limonite, goethite, raw and burnt sienna, caput mortuum and hematite. The present experimental work proposes a technique of differentiation that allows one to distinguish among all the different kinds of iron oxides, thereby providing a better understanding of the painting technique used on portable icons and wall paintings. The ratios between the main spectroscopic peaks, attributable to the major components usually present in ochres, were calculated and compared, one against the another, from the spectra obtained through micro-Raman spectroscopy. Elementary composition is also revealed through a scanning electron microscopy (SEM) analysis. The possibility for detailed study on a particular Byzantine ochre palette can thus be performed based on the small differences in its nature and composition. These differences can first be observed and then measured among all of the natural earth pigments, through microRaman and microFTIR spectroscopies.

Panselinos’ Byzantine wall paintings in the Protaton Church, Mount Athos, Greece: a technical examination

Abstract The sole surviving fresco paintings of Manuel Panselinos (13th century AD), one of the most celebrated Greek iconographers of the Byzantine era, are located in the Protaton Church (10th century AD) on Mount Athos, Greece. This paper presents an examination and technical analysis of 15 representative thematic scenes, covering an area of approximately 65 m 2 , from these monumental works of art. The following exhaustive study and documentation of both the original and the subsequently restored areas of the wall paintings were made possible by using various imaging techniques, including visible and ultra-violet photography, infrared reflectography, colour measurements and representation. The chemical identification of the pigments, binders and layer stratigraphy was achieved through the use of visible and ultra-violet fluorescence microscopy, micro-Raman spectroscopy, Fourier transform μspectroscopy (μFTIR), X-ray diffraction (XRD), and scanning electron microscopy with energy dispersive analysis (SEM-EDS) and electron probe microanalysis (EPMA). A collaborative analysis, its results demonstrate that the paintings were executed in both the true fresco and lime-painting techniques. They have also established Panselinos’ choice of materials and colour palette. We believe this study to be an important and necessary prerequisite for the future preservation and restoration of these unique frescoes.

Comparison of extraction methods for the analysis of natural dyes in historical textiles by high-performance liquid chromatography

Different methods for the extraction of Dactylopius coccus Costa, Rubia tinctorum L., Isatis tinctoria L., Reseda luteola L., Curcuma longa L. and Cotinus coggygria Scop. from wool fibres are investigated using high-performance liquid chromatography with diode array detector (HPLC-DAD). The efficiencies of five extraction methods which include the use of HCl (widely used extraction method), citric acid, oxalic acid, TFA and a combination of HCOOH and EDTA are compared on the basis of the (a) number, (b) relative quantities, measured as HPLC peak areas and (c) signal-to-noise ratios (S/N) of the compounds extracted from the wool substrates. Flavonoid glycosides and curcuminoids contained in R. luteola L. and C. longa L., respectively, according to liquid chromatography with mass spectrometry (LC-MS) identifications, are not detected after treating the fibres with HCl. All the other milder methods are successful in extracting these compounds. Experiments are performed using HPLC-DAD to compare the HPLC peak areas and the S/N of the following extracted compounds: indigotin, indirubin, curcumin, demethoxycurcumin, bisdemethoxycurcumin, fisetin, sulfuretin, luteolin, luteolin-7-O-glucoside, apigenin, carminic acid, alizarin, puruprin and rubiadin. It is shown that the TFA method provides overall the best results as it gives elevated extraction yields except for fisetin, luteolin, apigenin and luteolin-7-O-glucoside and highest S/N except for fisetin and luteolin-7-O-glucoside. It is noteworthy that treatment of the fibres with the typical HCl extraction method results overall in very low S/N. The TFA method is selected for further studies, as follows. First, it is applied on silk dyed samples and compared with the HCl method. The same relative differences of the TFA and HCl methods observed for the wool dyed samples are reported for the silk dyed samples too, except for rubiadin, luteolin and apigenin. Thus, in most cases, the nature of the substrate (wool or silk) appears to have negligible effects on the relative difference of the two extraction methods. Second, the selected TFA method is applied to treat wool and silk historical samples extracted from textiles of the Mamluk period, resulting in the identification of several colouring compounds. In all extraction methods mentioned above, DMSO is used to dissolve the dyes, after acid treatment.

Identification of Red Natural Dyes in Post‐Byzantine Icons by HPLC

Abstract A high performance liquid chromatography (HPLC) methodology, combined with UV‐Vis Diode Array Detection, is developed for the separation and identification of five reddish natural dyestuffs: cochineal, madder, lac dye, dragon blood, and brazilwood. The method is used for the identification of organic dyes in extracts originating from five icons, four of which are representative for the post Byzantine era (15th to 19th century) and one is typical for the Byzantine coloring technology (created at the 14th century). The origin and the nature of the coloring content of Mediterranean art objects, created in these historical periods are not well known. Carminic acid, the main active, coloring, ingredient of cochineal was identified in four icons, including the one of the 14th century. Brazilwood was found to be the only organic colorant in one icon of the post Byzantine era. It was also present, in addition to cochineal, in the icon of the Byzantine period. Further discussion, associated with the dyestuff origin, is provided based on the analytical results and the available historical data.

Phytochemical analysis of young fustic (Cotinus coggygria heartwood) and identification of isolated colourants in historical textiles

Young fustic (Cotinus coggygria Scop.; Anacardiaceae) has been used as a dyestuff since antiquity. Phytochemical investigation of the methanol extract of the heartwood has led to the isolation and structure elucidation by nuclear magnetic resonance and mass spectrometry (MS) of 3′,4′,6-trihydroxyaurone (sulfuretin) and 3′,4′,7-trihydroxyflavonol (fisetin) as well as 3′,4′,7-trihydroxyflavanol (fustin), 3′,4′,5,7-tetrahydroxyflavonol (quercetin), 3′,4′,5,7-tetrahydroxyflavanol (taxifolin), 4′,7-dihydroxyflavanol, 3′,4′,7-trihydroxyflavanone (butin), 4′,7-dihydroxyflavanone (liquiritigenin), trans-2′,3,4,4′-tetrahydroxychalcone (butein), 4′,5,7-trihydroxyflavanone and trans-2′,4,4′-trihydroxychalcone (isoliquiritigenin). The isolated compounds were used as reference materials for the development of a high-performance liquid chromatography–diode array detector–MS method, which was then applied to analyse (1) fresh silk samples dyed with young fustic, (2) dyed silk subjected to artificially accelerated light ageing and (3) historical silk micro-samples, extracted from ecclesiastical post-Byzantine garments (fifteenth to eighteenth century), which belong to monasteries of Mount Athos. Sulfuretin and fisetin, which are usually used as markers for the identification of the yellow dye and, for the first time, some of the aforementioned flavonoid components of young fustic were identified in the historical extracts. Furthermore, preliminary experiments suggested that although the amounts of the dye components decrease with light ageing, the relative ratio of fisetin and sulfuretin, after a first step of ageing, seems to be almost unaffected by such degradation processes raised by light. The effect of the latter on the morphology of the dyed silk fibres is briefly investigated by scanning electron microscopy.

Electrochemical study of aluminium ion reduction in acidic AlCl3-n-butyl-pyridinium chloride melts

AbstractElectrochemical reduction of AlCl3 dissolved in acidic AlCl3-n-butyl-pyridinium chloride melt was studied by linear sweep voltammetry and chronopotentiometry at tungsten and platinum electrodes, in the Al2Cl7− concentration range 0.3 to 0.5 M between 30 and 60°C. Al2Cl7− bulk reduction was preceded by a nucleation (tungsten) or alloy formation phenomenon (platinum). The overall results agree rather well with the mechanism:

An extensive non‐destructive and micro‐spectroscopic study of two post‐Byzantine overpainted icons of the 16th century

\begin{gathered} 2AlCl_4^ - \rightleftarrows Al_2 Cl_7^ - + Cl^ - \hfill \\ 4Al_2 Cl_7^ - + 3e \rightleftarrows Al + 7AlCl_4^ - \hfill \\ \end{gathered}

Investigation of the colourants used in icons of the Cretan School of iconography.

The electrochemical reaction appeared quasi-reversible. Calculated values of the product of the transfer coefficient by the number of the electron exchanged in the rate determining step were in the range 0.45 to 0.7. Diffusion coefficients for Al2Cl7− were calculated.