Non‐invasive and non‐destructive Raman spectroscopic characterization of some Brazilian ethnographic resins

Abstract

AbstractThe chemical investigation of museum collection items can provide key information on the provenance and technical aspects involved in their production and, additionally, can help in the establishment of restoration and conservation strategies of rare or valuable assets. Natural organic materials are challenging because of their chemical complexity and expected degradation. In this work, eight ethnographic resins from different sites in the Amazon and central areas in Brazil were studied by FT‐Raman spectroscopy aiming at the non‐invasive and non‐destructive identification of their chemical composition; chromatographic methods (Thin Layer Chromatography and Gas Chromatography–Mass Spectrometry—TLC and GC‐MS, respectively) were used as destructive confirmatory techniques. The samples were classified into five groups, each one presenting a common set of spectroscopic features: diterpenoid resins with chemical composition similar to the Brazil copal in some cases with carotenoids in their composition as did the triterpenoid resins also identified. Additionally, two gums (polysaccharides) were detected, and two very dark samples only generated a thermal or a luminescent background (1064 and 632.8 nm excitation, respectively). Total ion current (TIC) chromatograms from these very dark samples only showed peaks assigned to fatty acids probably because the resinous compounds were not soluble in the solvent used in GC‐MS analysis. These results show that resin‐containing museum assets in the Brazilian ethnographic context can be studied directly by Raman spectroscopy, contributing to a better understand of the culture of indigenous peoples from resin provenance, uses and processing for example. The results will be used as a database to be compared with certified reference samples, when available.