Colorful chemistry - American Chemical Society

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Colorful chemistry A request to teach a science course leads a chemist to the analysis of medieval pigments and ancient dyes.

ary Virginia Orna at the College of New Rochelle credits her younger brother for introducing her to chemistry. When Orna was 10 years old, her brother was presented with a chemistry set. Orna recollects, “As soon as I saw [the set], I said, ‘I want that.’ Since I happened to be bigger than [my brother] at the time, it was a hostile takeover.” Her enjoyment of the chemistry set and an inspirational high-school teacher led Orna to pursue chemistry. After she earned her Ph.D. from Fordham University, she entered the Order of St. Ursula; for three years she pursued theological studies before pronouncing her vows in the Order. Orna joined the faculty of the College of New Rochelle to teach chemistry after she obtained a master’s degree in theology as part of her studies to become a religious sister. One day, the chairperson of the art department approached Orna. It seemed that a number of students with art majors were intimidated by science courses. The chairperson asked Orna whether she could develop a course that would demonstrate that science and art are intertwined. Orna said, “Yes.” Orna realized that color and materials science were the two things common to science and art. She chose to focus on color and, in order to learn more about it, spent a sabbatical year at the Institute of Fine Arts at New York University. There, she made the acquaintance of an art history professor, Thomas Mathews. Mathews at that time was tremendously excited by a discovery he had made in the Special Collections of the

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COURTESY OF MARY VIRGINIA ORNA

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A chemist and a teacher. Mary Virginia Orna, after years of researching compositions of medieval pigments, now focuses on educational programs in the history of chemistry.

University of California, Los Angeles. He had found an early 14th-century Armenian manuscript, the Glajor Gospel Book. Orna remembers, “[Mathews] said it was the find of the decade [because] they hadn’t known it existed.” The manuscript contained miniatures in the styles of more than one painter and were distinctive enough to be discernable. But the question was whether the manuscript actually contained pigments from separate palettes. To answer the question, Mathews asked Orna to help determine the chemical compositions of the pigments. By using various spectroscopic analyses, Orna and Mathews ultimately demonstrated that the

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Glajor Gospel Book indeed contained a wide range of palettes and pigment qualities from five manuscript painters (Stud. Conserv. 1981, 26, 57–72). Orna and Mathews continued to analyze medieval Armenian and Byzantine manuscripts. Meanwhile, as they read medieval artists’ manuals, they found a plethora of recipes for blue pigments— almost to the neglect of other colors. They did a bit of investigation and discovered something interesting. “In the Middle Ages, there were only two blue pigments available that were naturally occurring,” explains Orna. One was ultramarine, which was extracted from the semiprecious stone lapis lazuli; the other was azurite, a copper carbonate-based mineral. Because these were the only natural sources of blue pigment, they were very expensive. “We found both ultramarine and azurite in many manuscripts,” says Orna. “But we also found some manuscripts where the pages just had holes, [with] a brown edge around the holes.” Orna and Mathews surmised that blue pigments other than ultramarine and azurite had been used in the manuscripts and that the unknown pigments had decomposed and corroded the pages over the centuries. Orna describes the destruction: “[The pigment] would not only eat the page it was painted on, but [also] maybe 50 or 60 pages on either side of it!” Orna and Mathews guessed that the pigments were synthesized from harsh chemicals, as evidenced by the recipes in the artists’ manuals. The hypothesis led them to try to decipher recipes of syn© 2005 AMERICAN CHEMICAL SOCIETY

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same way that copper carbonates formed in the earth to produce azurite. The heat from the dung probably also helped the reaction take place. Orna’s work over a period of 15 years on medieval copper-based pigments earned her a Fulbright scholarship in Israel in 1994. Her scholarship was sponsored

MICHAEL W. COLLINS

thetic, copper-based blue pigments that were made in medieval times. Translating the Latin text of the recipes wasn’t the stumbling block for Orna. “I have a background in Latin and know the structure of the language and a fair amount of vocabulary,” she says. It was the handwriting that caused problems. Orna had to teach herself a crash course in paleography, the study of ancient handwriting. Because writing manuscripts in medieval times was so laborious and time-consuming, the monks made liberal use of abbreviations, which Orna had to learn to decipher. But, she quips, untangling handwriting maybe wasn’t all that difficult, “because I’ve been reading students’ handwriting [for] so many years!” The other obstacle in the recipes was a chemist’s nightmare. The measurements were in incomprehensible ancient units and, to boot, imprecise. “I had to look up all of these [ancient] measurements in a book by Maurice Crosland, who has written on ancient chemical language,” says Orna. “[The recipes] would say ‘take some,’ and it would say something like ‘very strong vinegar’. But what do you mean by ‘very strong vinegar’?” Pure substances did not exist in medieval times, so reproducibility was next to impossible. When a recipe called for a substance like ‘pure silver’, it would often actually be referring to an alloy that contained anything from 5% to 30% copper mixed with silver. It would be the copper in the silver alloy that would produce the blue pigments in the form of carbonates. Orna also says that because of the lack of pure substances, “There was no way you would ever have any form of stoichiometry.” Because of their imprecise nature, the recipes involved a lot of unconsumed reactants and unpredictable side reactions. However, one source of a pure substance turned up in some of the recipes that Orna and Mathews discovered. Some recipes “used ingredients such as hot horse dung in order to provide a reactant, carbon dioxide,” she says. The carbon dioxide, along with ammonia that was also released from dung, was pure. The carbon dioxide allowed basic copper carbonates to form in much the

Natural blue. The mineral azurite was a source for blue pigment in medieval times.

by the Hebrew University of Jerusalem, the Weizmann Institute of Science, and the Edelstein Center for the Analysis of Middle Eastern Textiles and Artifacts at the Shenkar College of Textile Technology and Fashion. She taught courses at the three institutions and did research on excavated materials provided by the Israel Antiquities Authority. For the research, Orna worked with Zvi Koren at the Edelstein Center on extracting and analyzing dyes from tiny samples of ancient textiles. The textiles ranged from 2000 to 5000 years in age. Orna and Koren used HPLC to extract the dyes from the textiles and then carried out spectroscopic analysis to determine the composition. Although most of the dyes were based on vegetables indigenous to the region, Orna said they did find evidence of dibromoindigo, also known as royal purple. Royal purple comes from shellfish. The dye is produced in a tiny gland buried under the shell of a particular mollusk of the Murex genus. “You need ~50,000 shellfish to make 1 g of the dye,” says Orna. In ancient times, extracting the dye was very labor-intensive, not to mention smelly. Only members of royalty could afford the slaves

needed to produce royal purple. Orna and Koren discovered royal purple in textiles excavated from the top of the fortress of Masada in Israel. “It was the site of King Herod’s safe haven,” says Orna. “He must have outfitted [the site] with clothes, food, and water because he thought he might have to flee there, as people were trying to murder him.” King Herod never used the safe haven, but his belongings were found there. Orna’s lack of Hebrew didn’t dampen her teaching efforts during her Fulbright scholarship. “The students all wrote their homework in Hebrew, and then I would have a friend sit down with me and read to me what they wrote. I would tell this person to correct such and such and then give the grade. The students never knew that I didn’t read Hebrew!” Orna had both Israelis and Palestinians in her classes, and she lived in the Christian quarter of the Old City of Jerusalem. Her environment was a constant reminder of the political turmoil in the region. “The thing that stands out most in my mind with my experience in Israel is how wonderful individual people were and how kind they were to me. At the same time, [I had] a feeling of hopelessness and despair that the political situation would never be resolved.” When her scholarship ended, Orna returned to the United States “with an awful lot of work!” She continued her teaching and her research on copperbased blue pigments. She proposed a symposium to be sponsored by the American Chemical Society’s archeological chemistry subdivision of the Division of the History of Chemistry. For a while, she served as the director of educational services at the Chemical Heritage Foundation. Orna has now chosen to focus on teaching and is busy developing study tours in the history of chemical sciences for an adult-education outreach program. But she still fondly remembers her first experiments in her childhood bedroom, making sulfur dioxide with a deflagration spoon, sulfur, and an alcohol lamp. Orna says, “Basically, if I didn’t have a brother, I would have never learned about chemistry at such an early age.” a —Rajendrani Mukhopadhyay

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