WEATHERING SURFACES ON CLASSICAL MARBLE SCULPTURES: ISOTOPIC AND X-RAY DIFFRACTION ANALYSES


We have proposed elsewhere the use of a minimally-destructive, integrated approach towards the provenance determination of classical marble sculptures, using stable isotope analysis, x-ray diffraction, grain-size determination, stylistic analysis, literary information, and archaeological data. Stable isotope analysis and x-ray diffraction require only a few milligrams of clean marble powder, which can easily be removed from unobtrusive parts of sculptures, many of which already have damaged surfaces. Care must be taken in sample removal, however, since weathered marble surfaces are likely to have altered crystalline properties and to have markedly different isotopic values. The alteration of both carbon and oxygen isotopes by just a few parts per thousand is more than sufficient to produce an erroneous source attribution.

Experimental work by others has suggested that marble crusts may be used as evidence for the antiquity of a particular sculpture if the isotopic and crystallographic values of both the crust and fresh marble are determined. We present a comparison of stable isotope and x-ray diffraction data for weathered and fresh marble samples from more than 30 individual sculptures. These data are interpreted in light of biologically and geochemically mediated alteration mechanisms, and some suggestions are made regarding sampling techniques for provenance analysis, and on the authentication of marble sculptures.