The Ring Monstrance from the Loreto treasury in Prague: handheld Raman spectrometer for identification of gemstones

Abstract

A miniature lightweight portable Raman spectrometer and a palm-sized device allow for fast and unambiguous detection of common gemstones mounted in complex jewels. Here, complex religious artefacts and the Ring Monstrance from the Loreto treasury (Prague, Czech Republic; eighteenth century) were investigated. These discriminations are based on the very good correspondence of the wavenumbers of the strongest Raman bands of the minerals. Very short laser illumination times and efficient collection of scattered light were sufficient to obtain strong diagnostic Raman signals. The following minerals were documented: quartz and its varieties, beryl varieties (emerald), corundum varieties (sapphire), garnets (almandine, grossular), diamond as well as aragonite in pearls. Miniature Raman spectrometers can be recommended for common gemmological work as well as for mineralogical investigations of jewels and cultural heritage objects whenever the antiquities cannot be transported to a laboratory. This article is part of the themed issue ‘Raman spectroscopy in art and archaeology’.

A database of Raman spectra of precious gemstones and minerals used as cut gems obtained using portable sequentially shifted excitation Raman spectrometer

“…Special situations are those when objects to be investigated cannot be moved, and fast and non‐destructive analysis is needed. This may apply also to gemstones or jewels, sometimes not allowed to be transported or borrowed for study in the lab . Interesting evolution and new trends for gemmological practice of jewellers and experts can be followed as well.…”

The first use of portable Raman instrumentation for the in situ study of prehistoric rock paintings in Patagonian sites

“…Moreover, handheld and palm‐sized instruments have typically a single, fixed grating, in comparison with portable Raman instruments . In some of the studies, handheld Raman instruments were used for detecting biomarkers in complex samples in a host geological matrix under Alpine conditions, for the in situ identification of arsenate minerals at outcrops, for field identification of several minerals, for the analysis of stones and gemstones mounted in the sceptre of the Faculty of Science of Charles University in Prague, and for detection of common gemstones in several complex religious artefacts and the Ring Monstrance from the Loreto treasury . At the latter study also, a 0.8‐kg palm‐sized device was used.…”

Comparison of seven portable Raman spectrometers: beryl as a case study

“…(top part), it is apparent that when the fluorescence background has a smooth and non‐complicated structure, the final spectrum that is a result of the fluorescence removal process applied on the three raw spectra at the top is very clean and with a completely flat baseline. All the Raman bands of emerald are located at correct wavenumber positions, and most importantly, no additional false bands are produced. This example is in a strong contrast to the Raman spectra obtained by the same instrument on the sample of synthetic emerald that can be seen in Fig.…”

“…[12] A light handheld Raman spectrometer (Rigaku) equipped with a 532-nm excitation laser was used for example to detect microbial pigments under outdoor conditions for halophiles research. [5] Few studies showed until now new possibilities of direct application of portable Raman spectrometers to detect gemstones or other minerals mounted in historical artefacts: Torah shield with quartz, agates, emerald, pearls and corals [13] ; an 18th century monstrance from Prague Lesser Chapucines Treasury with numerous diamonds, garnets, amethysts, emeralds [14] and rubies; and numerous 17th and 18th century Sicilian jewels (diamonds, garnets, amethysts emeralds and rubies) collected in the frame of the Messina regional museum. [15] Beryl and its varieties Beryl Be 3 Al 2 Si 6 O 18 , a hexagonal cyclosilicate with six-membered single rings, is the most common member of the beryl group (other minerals: bazzite, indialite, stoppanite and pezzottaite).…”