Noninvasive Multitechnique Analysis of Baroque Amber Artworks From Gdansk: The Benefits of Using Raman Spectroscopy

Abstract

The multidisciplinary, noninvasive analysis of baroque amber artworks is part of a research project that deals with the most valuable objects from the Museum of Gdansk (Poland). The two most interesting objects will be presented here: a Baroque Gdansk wardrobe-shaped amber cabinet (made by Johann Georg Zernebach, Gdansk, 1724) and a crucifix (Gdansk, 17th century). Macro- (UV, IR, and X-radiography) and micro- (XRF and Raman spectroscopy) analytical methods were applied to reveal traces of old conservation treatments and uncover the techniques of the 17th and 18th century amber masters. UV photography shows the differences between the amber plates that are not so easily detected under visible light, while XRF spectrometry detects elements atypical for amber objects, suggesting previous conservation treatments. Confocal Raman measurements, especially Raman depth profiling, were performed for the amber artworks and allowed to detect areas of previous conservation treatments. Single-point scans were collected from the surface (0 μm) to a depth of −200 μm, with a step of 50 μm. The results allowed us to identify three different types of zones: where the amber was preserved without any protective layer, places where the amber was covered with a thin layer of a protective substance, and places where amber elements were compensated for loss using a binding agent and filler. The presented project allowed the development of a comprehensive methodology for the analysis of amber objects, especially to optimize the capabilities of confocal Raman microscopy. The combination of macro- and microanalytical techniques made it possible to obtain a broad overview of such complex artworks while optimizing the time and effort spent on the investigations.