IDENTIFICATION OF BINDING MEDIA IN ART OBJECTS: PROTATON CHURCH WALL PAINTINGS AND N.GYZIS' PAINTINGS

• A. Tsakalof, K. Bairachtari, Sister Daniilia, I. Chryssoulakis ("Ormylia" Art Diagnosis Center, Sacred Convent of Annunciation, 63071 Ormylia-Chalkidiki, Greece)
• K. Bairachtari, I. Chryssoulakis (National Technical University of Athens, Department of Chemical Engineering, Iroon Polytechniou 9, 157 80 Zografou Campus, Athens, Greece)

Identification of binding media in art objects helps to recognize the materials used for the object creation and eventually contributes to the interpretation of the painting techniques. This information is valuable both to art historians and conservators. Currently a number of chromatography-based techniques are used for the binding media identification and namely GC, GC-MS, Py-GC-MS, DTMS, HPLC [1]. We present a sensitive and selective GC-MS based method for proteinaceous and lipid (drying oil) binding media identification and several examples of these method applications.

Materials and methods: ThermoQuest (USA) Polaris GCQ gas chromatograph- mass spectrometer (GC-MS) was employed in the research. The GC-MS was supplied with split/splitless injector and Alltech AT-5MS 30mx0.25mm capillary column. Two different procedures were followed for protein and lipid analysis. The protein analysis included the stages of proteins hydrolysis, silylation of the resultant amino acids followed by their GC-MS quantification. The identification of the proteinaceous binders (casein, egg, animal glue) was achieved by application of Principal Component Analysis (PCA) on the amino acid percentage content of the sample. The drying oils identification was based on the values of fatty acids ratios: palmitic to stearic (P/S) and azelaic to palmitic (A/P). Fatty acids were determined through sample saponification, free fatty acids isolation, their silylation and GC-MS quantification. The methods for protein and lipid analysis were validated by their applications to the analysis of the reference samples.

Results 1) Proteins analysis: sixteen amino acids are detected and fifteen are used for protein identification. The detection (LOD) limit of amino acid quantification lies in the range 25-75pg and consequently very small amount of sample (< 1mg) is needed for the analysis. The method was applied to the investigation of wall painting samples from the Protaton Church (Mount Athos, Greece) and revealed the use of egg tempera in the wall paintings. The presence of small amount of animal glue was also detected. The detailed results and their interpretation will be presented. 2) Lipids analysis: low LODs (6-35pg) were also achieved for the fatty acids quantification. The method was applied to the investigation of N.Gyzis' paintings and revealed the use of linseed oil in painting "The New Century" (A/P=1,6, P/S=1,2 , ÓD=50,2%) and poppy seed oil in the "Penelope Gyzis" (A/P=1,7, P/S =5,2, ÓD=59.8%). The interesting peculiarity of fatty acid analysis on ion trap GC-MS was observed. This refers to the formation of fatty acids adducts with water in mass analyzer. This fact substantially changes the way of fragmentation increasing the percentage of the base peak.

[1]. Tsakalof A.K., Sotiropoulou S., Chryssoulakis I. "Binding media identification in art objects: the state of art in Europe. Results of the international survey", 4th Congress of Acheometry, Athens, 2003.