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Spectroscopic Analysis of Museum Objects

Posted On January 06, 2017 | 16:14 pm | by lainw | Permalink
Dumbarton Oaks Collaborates with the Walters Art Museum

In preparing the forthcoming catalogue of Pre-Columbian objects from Central America and Colombia, Dumbarton Oaks has collaborated with the Walters Art Museum in the analysis of greenstone artifacts—primarily pendants and beads—from the Nicoya Peninsula and the Central Caribbean region of Costa Rica. Typically these objects are labeled as jadeite, but the team, including Bryan Cockrell, Colin McEwan, and Juan Antonio Murro from Dumbarton Oaks and Glenn Gates and Julie Lauffenburger from the Walters, sought to nuance our understanding of the objects’ compositions.

A number of minerals may be present in a greenstone object, and jadeite may be entirely absent. Atoms of one element may substitute for those of a different element in the crystal structure of the mineral, giving the material a range of colors. The team used two noninvasive techniques with equipment brought to the Dumbarton Oaks Museum study room—Raman spectroscopy and X-ray fluorescence spectrometry—in order to learn about the mineral and elemental compositions of forty greenstone objects in the collection. Raman spectroscopy involves the application of a laser beam to induce molecular vibrations in the material being studied; as a result, the frequency of the photons of the laser beam changes and is measured by a detector, revealing information about mineral composition. X-ray fluorescence spectrometry uses an X-ray beam to ionize atoms in the material, leading to the release of energy (fluorescence) that is characteristic of the material’s elemental composition.

The team is currently comparing this data to reference materials, but a number of objects have compositions different from those that have been ascribed to them in the past. There are greenstone sources known in Costa Rica, including serpentine, but so far not jadeite, while there are other sources in Guatemala and in the Caribbean. By combining mineral and elemental information and comparing it to published data, the team can work toward a longer-term goal of identifying the greenstone sources present among the objects.