Conference paper

Ziemann, Martin:

Ramanspektroskopie an Wandmalereiproben

High-resolution micro-Raman spectroscopy was used to study pigments and their alteration products in paint layers from five specially selected samples. Samples were taken from wall paintings in the former library on the 2nd floor of the cloister of the cathedral in Brandenburg / Havel, Germany. The aim was a detailed check of indeterminate results previously obtained by the application of the REM/EDX and portable XRF analytical methods to wall painting samples.
In order to identify pigment grains and secondary products that formed after transformation processes in the painting layers, polished cross sections of tiny sample flakes (few mm²) were used for micro-Raman measurements with an analytical focus diameter of 1-1.5 µm. The main results of the study largely confirm the findings of the REM/EDX analyses, but there are differences and corrections too. For example, instead of malachite as suggested by the REM/EDX data, atacamite was identified in sample P5 by Raman spectroscopy, where it forms the core of larger pigment grains. Both methods identified cumengite alteration rims on these big pigment grains. Further work by REM/EDX is needed to clear the question if the atacamite grain cores too are results of a transformation process, and whether the original paint material was malachite.
High-resolution micro-Raman spectroscopy is a powerful method that offers deep insights into pigment constituents, pigment transformations and the behaviour of paint layers of wall paintings with time.