New database describes all the marbles

Scientific detectives use atomic isotopes for more than tracking down the sources of drugs (see “Chemistry Catches Cocaine at Source” in this week’s issue: Chemistry Catches Cocaine at Source). With a new database of isotopic ratios measured in samples of Greek marble, researchers can identify the quarries that supplied the stone for some of Europe’s most famous statues and architecture.

More than 150 quarries dot the southern slopes of Greece’s Mount Pentelikon, which lies about 18 kilometers northeast of Athens. These sites have been a primary source of white marble for the eastern Mediterranean region for the past 2,500 years.

Archaeologists and art historians typically have tried to identify the specific sources of the marble by examining such factors as the rock’s texture or the size of its mineral grains, says Scott Pike, a geologist at Emory University’s Oxford College in Oxford, Ga. In the 1970s, scientists began efforts to discriminate varieties of marble by measuring the respective ratios of carbon and oxygen isotopes in the rock. At the time, their database was limited because documented samples from historically important sites were scarce.

With the cooperation of the Greek Ministry of Culture, Pike has collected about 1,000 samples from all of the quarries on Mount Pentelikon, including those that operated in ancient times. Analysis of more than 600 samples showed isotopic fingerprints that could enable scientists to distinguish among small groups of the quarries. Pike presented his findings this week in Reno, Nev., at the 112th annual meeting of the Geological Society of America.

Information on the sources of marble can answer a variety of scholars’ questions, Pike says. Archaeologists could use the database to piece together ancient trade routes, for instance. Knowing when certain quarries were active can help art historians date buildings and statues.

Isotopic analysis can also provide clues about sculptors and where they were working, says John J. Herrmann Jr., an art historian at the Museum of Fine Arts in Boston. He recently used the technique on a small Italian statuette, carved in a classical style, that he believed could have been part of a Greek architectural relief. His analysis showed that the statuette actually had been carved from Carrara marble quarried in Italy. This indicates that the sculptor might have been an Italian who carved in the Greek style or a Greek who moved to Italy and worked with locally available material.

Isotopic analysis could help historians identify modern forgeries as well, Herrmann notes. Also, because the ratios of carbon and oxygen isotopes tend to be especially consistent in a given hunk of marble, with this technique researchers could match objects carved from the same block of stone.

“[Pike’s] database is a tool that can be applied in many different ways,” Herrmann says. “We [art historians] don’t know where it’ll take us.”