Gemstones and noble metals adorning the sceptre of the faculty of science of charles university in prague: Integrated analysis by Raman and XRF handheld instruments

摘要

A commonly marketed handheld Raman spectrometer showed excellent possibilities in being used as a key instrument for unambiguous identification of gemstones mounted in the sceptre of the Faculty of Science of Charles University in Prague from the mid-20s of the 20th century. Numerous SiO _2 forms including chalcedonies intermixed with moganites (e.g. moss agates and carnelians), amethysts, citrines as well as garnets (pyrope-almandines) were identified. The estimation of the garnet type was based on obtained Raman parameters. The individual minerals constituting the lapis lazulis could not be discerned because of very high fluorescence they exhibited in the fingerprint region of the Raman spectrum, nevertheless the positions of the observed peaks in the 1000-2000cm-1 area were in very good agreement with the values of commercially available lapis lazuli pigment. The noble metals of the sceptre were studied by means of X-ray fluorescence analysis, which confirmed the presence of silver alloys and gilding. The comparison of silver alloys' semiquantitative analysis with the expected fineness, denoted by the hallmarks, indicated silvering. This has been later confirmed by the newly discovered restoration documentation. Portable handheld Raman and X-ray fluorescence instruments represent an ideal tool for studying historical artefacts, where an in situ investigation in museums or similar sites is obligatory.