(A) “Portrait of a Bearded Man” (Walters Museum of Art # 32.6), dated c. 170-180 Roman Empire from Egypt; (B) Portrait under ultraviolet light. The purple keyboard on the shoulders looks pinkish-orange with an arrow. Credit: Walters Museum of Art
Scientific analysis of ancient portrait pigment reveals long-lost artistic details.
How much information can you get from a purple pigment that is not larger than the diameter of a hair torn from an Egyptian portrait that is about 2,000 years old? Plenty for a new job. Analysis of this stain can give us some information about how the pigment is made, what it is made of, and perhaps the people who created it. Research International Journal of Ceramic Engineering and Science.
“We are very interested in understanding the meaning and origin of portraits and finding ways to combine them, and first and foremost in a cultural understanding of why they are painted that way,” says Darryl Butt, a materialist and co-author of the College of Mining and Earth Sciences.
Faiyum mummies
The portrait, which contains purple pigment, came from an Egyptian mummy, but it doesn’t look the same as you might think of a mummy at first – it doesn’t look like Tutankhamen’s golden shroud, the paintings on the walls and the edges. papyrus. Not like Boris Karloff.
The Portrait of the Bearded Man dates back to the second century, when Egypt was a Roman province, so the portraits are more vivid and less hieroglyphic than the Egyptian art of earlier times. Most of these portraits are from a region called Faiyum, and it is known that there are about 1,100 people. The wood was painted and wrapped in sheets holding the mummified body. The portraits were intended to express the identity of the person, as well as their status – either factual or voluntary.
The idea of this status is actually very important in this situation, because the man in the portrait we are focusing on wears purple marks Vinegar his buckle. “Because of the purple pigment clavi-In ancient Rome, a purple mark on a toga that showed the rank of senator or horseman – we thought we might increase its importance in the afterlife, ”said Glenn Gates of the Walters Museum of Art in Baltimore, where the portrait lives. .
Butt says that purple is considered a symbol of death in some cultures and life in others. It was associated with royalty in ancient times and still exists today. Butt, paraphrasing author Victoria Finlay, says she can suggest the end of the known and the beginning of the unknown with purple at the end of the visible color spectrum.
“So the purple color in this portrait surprised us what it was and what it meant,” Butt said. “Purple stimulates many questions.”
An enlarged detail of the left keyboard shows a large purple pigment particle that looks like a rough stone. Credit: University of Utah
Lake pigments
Under a microscope, Gates saw that the pigment resembled crushed stones, which contained particles that were tens to hundreds of times larger than typical paint particles. To answer the question of how this was done, Gates sent a portion of the pigment to Butt and his group for analysis. The particle was only 50 microns in diameter, about the same as a human hair, making it difficult to follow.
“The piece was sent to me from Baltimore, stacked between two glass slides,” Butt said, “and it took two days to find it because it moved about a millimeter during transit.” To transfer the fabric to a sample holder, the group used an eyelash with a small amount of glue on the tip for transfer. “The process of analyzing something like that is a bit like an operation.”
With this particle, no matter how small, researchers can make smaller samples using a focused ion beam and analyze these elements according to their elemental composition.
What did they find? You need to know how dyes and pigments are prepared to put the results into context.
Pigments and dyes are not the same thing. Dyes are pure dyes, and pigments are a combination of dyes, minerals, binders, and other components that make up what we know as dyes.
Initially, purple dyes came from a diaper of sea snails Murex. Butt and colleagues assume that the purple used in this mummy painting is something else – synthetic purple.
Researchers also speculate that synthetic purple colors can be detected by chance when red dye and blue indigo dye are mixed. The final color may also be due to the addition of chromium to the mixture.
From there, the mineralogy of the pigment sample suggests that the pigment is mixed with clay or silicon material to form a pigment. According to Butt, a talented artist, pigments made in this way are called lake pigments (derived from the same root word as lacquer). In addition, the pigment was finally mixed with wax binder before being painted on the linden tree.
An example of a pigment showing the layer within a particle. Credit: University of Utah
The pigment showed evidence of a crystal structure in the pigment. “Lake pigments were thought to be crystalline-free before this work,” Gates said. “We already know that lake pigments have crystalline domains, and they can work to” trap “environmental evidence when a pigment is formed.”
The bottom of the barrel, husband, tank
Another detail added a little more depth to the story of how this portrait was made. Researchers also found large amounts of lead in the pigment, and linked these findings to the observations of a British researcher in the late 1800s who said that paint tanks were made of lead in the workshops of Egyptian painters.
“Over time, a story or hypothesis emerged,” Butt said, “indicating that Egyptian painters produced red paint in these lead tanks.” At the end of the day, after being painted, he says, there may be a purple slime in the bucket. “Or they were very smart and we may have found a way to change the color to purple by adding salt to the transition metals and not taking the red paint. [a substance that fixes a dye] to intentionally synthesize a purple pigment. We don’t know. ”
Broader effects
This is not the first time Butt has used scientific methods to study ancient art. Involved in similar previous research and built on both research and artistic roots to develop a class called “Art Science” that covers research and discussion on various historical works on history and topics related to reverse engineering. pioneer newspapers to ancient art.
“Mixing science and art is just fun,” he says. “It’s a great way to make learning science more accessible.”
And there are broader effects of the work. There is relatively little information about mummy portraits, including whether the same artist painted more than one portrait. Analyzing pigments at the atomic level can provide the chemical fingerprint needed to bond the portraits together.
“Our results offer a tool to document similarities in the time and place of production of mummy portraits, as most are peeled from the cemetery and lack the archaeological context,” Gates said.
“So we can close families,” Butt added. “We can connect artists.”
Reference: Glenn Gates, Yagiao Wu, Jatuporn Burns, Jennifer Watkins, and Darryl P. Butt, “Microstructure and Chemical Characteristics of a Purple Pigment from a Portrait of a Faiyum Mummy,” October 28, 2020, International Journal of Ceramic Engineering and Science.
DOI: 10.1002 / ces2.10075