Kolloquium

Datum

26.01.2022

Zeit

13:00 - 14:00

Sprecher

Maram Naes (TU Berlin)

Sprache

en

Hauptthema

Materialien

Beschreibung

Probing Chemical and Micromorphological Properties of Gold in Historical Wall Paintings Using Lab and Synchrotron Investigation Methods Zoomraum: Meeting-ID: 873 3900 4773 Kenncode: 035976 Abstract: Gilding materials and technology of Nabataean gilded wall paintings dating back to the 1st century AD were identified using various spectroscopic techniques. Micro-spectroscopic analytical investigations were performed on wall painting and stucco fragments from various painted facades in Petra. Non-invasive (NI) and non-destructive (ND) analytical methods were prioritised in our investigation approach. Beside Optical Light Microscopy (OM) and Environmental Scanning Electron Microscopy (ESEM), 2D and 3D Micro X-Ray Fluorescence (µXRF) with laboratory and synchrotron sources were utilized. 2D elemental mapping of major components allowed the detection of visually invisible (to bare eye) nanogold clusters. Moreover, laboratory and synchrotron Fourier Transform Infrared Spectroscopy (FTIR) were used to investigate the molecular composition of the gilded samples. Chemical speciation of gold and iron in the historical samples were also studied using NI and ND X-Ray Absorption Spectroscopy, both Near Edge (XANES) and Extended (EXAFS). The results allowed defining gilding technology in Nabataean gilded wall paintings and stucco and categorising the paintings accordingly. Results showed that gilding materials and techniques did influence the current condition of gold layer at both macro and micro scales. A micrographic glossary of gold’s layer micromorphology was developed and correlated with various deterioration mechanisms. Remarkably, gold and iron speciation in the historical samples is found to be influenced by both composition and condition of the gilded painted surfaces. EXAFS analysis at Au-L3 edge (11.919 eV) allowed the detection of various gold species indicating possible reactions with iron oxide paint layer as well as inherent and surrounding soluble chloride salts. Iron speciation showed the presence of various iron oxides and sulfates in relation to composition and condition. Thermal influence (uncontrolled fire event in site’s history) on its oxidation state was evident in the pre-edge region at 7.1135 keV. These findings are reported for the first time in historical gilded paintings, certainly Nabataean. A selection of our results will be presented in this webinar.

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Letztmalig verändert: 06.01.2022, 11:51:23