SCIENCE & TECHNOLOGY
BLUE WHODUNIT ARTIFACT-STAINING DYE structures revealed, but case far from closed CARMEN DRAHL, C&EN WASHINGTON
THIS WINTER, Gilberto Artioli’s team re-
LUIGI PECORA/ANSA
ported the structures of three new pigment molecules. Because the molecules came from samples that originated near Verona, Italy, the University of Padua geoarchaeologist named two of the brilliant blue dyes after Verona’s Shakespearean star-crossed lovers, Romeo and Juliet. Artioli’s dyes are also the protagonists of a drama of their own. And for some researchers, things might have been better if the pigments had never existed. Artioli’s samples came from prehistoric flint tools that last year began showing very visible signs of contamination—a bright blue tinge. The mystery sparked a furor in Italy and in the archaeology community (Nature, DOI: 10.1038/466306a; ScienceInsider, July 22, 2010). In ensuing media coverage, the case became as much about finding human culprits for the damage as about finding chemical ones. “Flint stones are commonly rather unreactive materials,” so the blue cast was especially puzzling, Artioli says. With bluestained flint samples supplied by Laura Longo, then-curator of Verona’s Natural History Museum, and by the regional office of Italy’s Ministry of Culture, Artioli, analytical chemist Andrea Tapparo, and colleagues set to work. Their earliest tests detected contamination with hydrocarbons but didn’t turn up any colored molecules. Because surface analysis wasn’t yielding any clues, the team decided to look a little deeper. They used warm acetone to extract the blue compounds from a flint sample. High-performance liquid chromatography purification and structural identification nabbed the three pigment perpetrators— Romeo blue, Juliet blue, and flint blue (Anal. Bioanal. Chem., DOI: 10.1007/s00216-010-4625-4). The trio belongs to the triphenylmethane dye family, an old class of syn-
2,2,4-trimethyl-1,2-dihydroquinoline, somehow desorbed from the mats to the tools and trimerized to form the blue contaminants. It’s not yet clear how that happened, Artioli says. The flint’s silica surface could be involved, but his team thinks it’s more likely that iron species from inclusions in the flint catalyzed the reaction because the intensity of the blue discoloration lines up with the inclusions in microscope images.
thetic colorants that counts the pH indicator bromocresol green among its members. Along with the structure identification, the Padua team’s work provides a possible explanation for the blue sheen, which “I’VE BEEN ACTIVE in [conservation] for 15 cropped up after the ancient artifacts were years, and it’s the first time I’ve seen somemoved in 2007 and 2008 to a former milithing like this,” says Francesca Casadio, a setary armory when their original home—an nior conservation scientist at the Art Insti18th-century castle used as a storage site for tute of Chicago. Artioli’s team “does a very the museum—was sold to good job in characterizing the dyes raise funds. and proposing what the precursor OUT OF THE BLUE They say that an addimay be,” she adds. Museum conLucia Cametti, tive from synthetic rubber servation experts typically envision president of Verona’s mats in the armory storage Committee of Culture, detrimental effects of packing and cabinets is the source. That storage materials in terms of corholds one of the blue flints on July 14, 2010. rosion, discoloration, or formation additive, the antioxidant of white or colorless deposits, not unusually vivid colors as in this case, she explains. Furthermore, “we would be more concerned with metallic, plastic, or wooden objects than with stone,” she adds. The stone tools remain in the armory, but the regional office of the Ministry of Culture has asked museum officials to remove the rubber mats on the basis of Artioli’s recommendation, says Vincenzo Tiné, the regional supervisor of the ministry. Tests are ongoing to confirm Artioli’s work and to determine whether bacteria from the flint’s surface contributed to the blue dye formation, he adds. To Longo, who is now director of culture for the municipality of Florence after resigning from her position with the Verona museum in December 2010, those actions come as too little, too late. She says Italian law requires rigorous environmental testing prior to moving artifacts, and testing should have been done when relocating these to the former military armory, which was not explicitly designed for sensitive specimens. Longo was on leave from the museum from 2005 to 2009 and was not involved with the move. She was suspended without salary from her curator post in July 2010 WWW.CEN-ONLINE.ORG
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after complaining that the tools hadn’t been properly transferred. “We have very strict laws for cultural heritage in Italy,” Longo says. “We know exactly + + + what we have to do when we N N N NH NH NH H H H move collections or when we lend archaeological material for exhibitions. So you cannot say Juliet blue Romeo blue Flint blue ‘Oh, I forgot’ or ‘I didn’t know.’ ” Longo notes that Neanderthal bones in the same collection as the stained tools were N CHEMICAL CULPRITS Formed from the dihydroquinoline once used in studies of NeanderH at left, Romeo blue and flint blue differ from Juliet blue in their thal DNA (Science, DOI: 10.1126/ 2,2,4-Trimethylunsaturation (differences highlighted in red). science.1147417). To the best of 1,2-dihydroquinoline her knowledge, the bones and other items in the collection didn’t turn blue, but that doesn’t mean they prehistoric collection be transferred out of The story “makes a strong argument for weren’t chemically contaminated and their the armory to a safer place and that parties fostering interdisciplinary research that scientific value compromised as well, she responsible for damaging the artifacts be can bring a more scientific grounding to says. “Can we rely on the results from any identified. Last summer, eminent archaestoring works of art,” Casadio says. “We’ll new studies on these materials?” ologists and paleoanthropologists signed a still have unexpected events, but we can try Artioli’s team is still trying to determine similar petition. And Verona’s chief public to develop more preventive conservation whether the blue discoloration can be prosecutor is reviewing evidence to determeasures.” reversed. And Tiné says that tests from mine whether crimes have been committed “Care and precaution in conservation Verona’s regional occupational safety and under Italy’s cultural heritage laws. are never excessive,” Artioli adds. ■ health administration have ruled out the possibility of environmental pollution in the armory. “Nobody could foresee that stone materials that have crossed entire eras would have suffered from contact with the soft materials accommodating them,” Tiné says. The tale “teaches us how little we yet know about the complex interactions between storage environment and archaeological items.” MUSEUMS CAN’T always predict the ef-
fects that a change will have on their exhibits because they deal with a wide array of materials, Casadio says. In the art field, it’s common in the U.S. and the U.K. for museum scientists to test new materials, from gaskets to packing crates, which are to be put in contact with collections. The typical procedure, called an Oddy test, places the material to be tested in a warm, humid environment with metal strips as indicators. These conditions accelerate corrosion or other damage that the material or any compounds it emits might cause, she explains. “It’s a pretty low-tech method,” and researchers are seeking better alternatives, she says. “But it’s a first line of defense.” The case of the blue flint is still far from closed. The Italian press reports that on March 7, two senators in Italy’s Parliament introduced a petition to Sandro Bondi, Italy’s minister of culture, demanding that the WWW.CEN-ONLINE.ORG
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