Stable Carbon and Oxygen Isotope Sourcing of Marble Sculptures in the Museum of Fine Arts, Boston

We have measured the stable carbon and oxygen isotope ratios of 75 marble sculptures in the collection of the Museum of Fine Arts in Boston. The results were compared with published isotopic data for Mediterranean marble quarries and also with unpublished data produced by Herz. For about one piece in four, the quarry source can be unequivocally identified on the basis of two isotope ratios alone. In the rest of the cases, overlapping data fields of isotope ratios produce, on average, four possible solutions to the question of marble source. For 18 sculptures, the material could be identified as dolomitic marble on the basis of visual inspection and X-ray diffractometry. This additional evidence allowed unequivocal source identifications to be made. Other mineralogical data, archaeological and literary evidence, as well as stylistic analysis similarly help to narrow the choices among overlapping isotope data fields.

For 11 pieces, the isotope ratios of patinated surfaces were compared with those of the unaltered interiors, samples being available from fresh breaks. Significantly, the surfaces of only four pieces showed appreciable isotopic alteration.

In many instances, marble source identifications arrived at by traditional methods of informed visual inspection were gratifyingly confirmed by our technical procedures. In others, they were spectacularly wrong. We will comment on some notable cases and will also suggest that three or more isotope ratios could provide unequivocal source identifications where two isotope ratios fail. Experience with such unrelated materials as elephant ivory and rhinoceros horn suggest that stable strontium isotopes should do the trick, but the quarry database would be costly to construct.