Evaluation of a Portable Sequentially Shifted Excitation Raman Spectrometer for Applications in Art and Archaeology

Abstract

Raman spectroscopy is a rapid, in situ, non-destructive analytical technique that is commonly used in cultural heritage applications, but conventional Raman spectroscopy often faces problems posed by sample transportation and fluorescence. Bruker’s BRAVO handheld Raman spectrometer, with a proprietary sequentially shifted excitation fluorescence reduction algorithm, has been used as a tool for characterizing cultural heritage materials by art historians and archaeologists, yet its capabilities have not been fully evaluated. We use three approaches to assess BRAVO’s applicability for analyzing cultural heritage materials. First, we compare spectra of reference minerals, including minerals of artistic interest and from a wide variety of mineral groups, acquired on both BRAVO and a benchtop system. We find that, in contrast to a benchtop unit, BRAVO allows for characterization of large or difficult-to-transport samples, mitigation of fluorescence and etaloning, analysis of phyllosilicates, and bulk characterization of mixtures. However, the device encounters challenges posed by the difficulty of sample positioning, the impracticality of handheld use, artefacts from fluorescence reduction, the large laser spot size, the limited spectral resolution and range, and the broadening of peaks. Second, we analyze pigments from the conservation laboratory at Princeton University Art Museum and find that BRAVO is useful for identifying samples whose labels are ambiguous or incorrect. Third, we identify pigments in three objects from the Art Museum as a demonstration of BRAVO’s potential cultural heritage applications. In total, this study suggests that, despite its limitations, BRAVO is a useful tool within the fields of art and archaeology.