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How much information can you get from a speck of purple pigment, no larger than a hair’s diameter, plucked from an Egyptian portrait that is nearly 2,000 years old? Many, according to a new study. Analyzing that grain can teach us how the pigment was made, what it’s made of and maybe even a little about the people who made it. The study is published in International Journal of Engineering and Science of Ceramics.
“We are very interested in understanding the meaning and origin of portraits and in finding ways to connect them and find a cultural understanding of why they were painted in the first place,” says materials scientist Darryl Butt, co-author of the study and dean of the College of Mines and Earth Sciences.
Faiyum mummies
The portrait that contained the purple pigment was from an Egyptian mummy, but it doesn’t look the same as what you might initially think of as a mummy, not like Tutankhamun’s gold sarcophagus, nor like the side paintings on the murals and papyri. Not like Boris Karloff, either.
The portrait, called “Portrait of a Bearded Man”, dates back to the second century when Egypt was a Roman province, so the portraits are more realistic and less hieroglyphic than Egyptian art from earlier times. Most of these portraits come from a region called Faiyum, of which around 1,100 are known to exist. They are painted on wood and were wrapped in the linen that contained the mummified body. The portraits were intended to express the likeness of the person, but also their status, real or ambitious.
That idea of status is actually very important in this case because the man in the portrait we’re focusing on wears purple markings called Vinegar on his toga. “Since the purple pigment occurred in the Vinegar – the purple mark on the toga that in ancient Rome indicated senatorial or equestrian rank – it was thought that perhaps we were seeing an increase in the subject’s importance in the afterlife, “says Glenn Gates of the Walters Art Museum in Baltimore, where the portrait resides .
The color purple, Butt says, is seen as a symbol of death in some cultures and a symbol of life in others. It was associated with royalty in ancient times, and still is today. Paraphrasing author Victoria Finlay, Butt states that purple, located at the end of the visible color spectrum, can suggest the end of the known and the beginning of the unknown.
“So the presence of purple on this particular portrait made us wonder what it was made of and what it meant,” says Butt. “The purple color stimulates many questions”.
Lake pigments
Through a microscope, Gates saw that the pigment looked like shattered gems, containing particles ten to a hundred times larger than typical paint particles. To answer the question of how this was done, Gates sent a particle of the pigment to Butt and his team for analysis. The particle was only 50 microns in diameter, about the same as a human hair, which made it difficult to keep track of.
“The particle was shipped to me from Baltimore, sandwiched between two slides,” says Butt, “and because it had moved about a millimeter in transit, it took two days to find it.” To move the particle onto a sample holder, the team used an eyelash with a small amount of adhesive on the tip to make the transfer. “The process of analyzing something like this is a bit like doing surgery on a flea.”
With that particle, however small, the researchers were able to process even smaller samples using a focused ion beam and analyze those samples for their elemental composition.
What did they find? To put the results in context, you need to know how dyes and pigments are produced.
Pigments and dyes are not the same. Dyes are the pure coloring agents and pigments are the combination of dyes, minerals, binders and other components that make up what we might recognize as paint.
Initially, the purple dyes came from a gland of a genus of sea snails called Murex. Butt and his colleagues speculate that the purple used in this mummy painting is something else: a synthetic purple.
The researchers also speculate that synthetic purple may have originally been discovered by accident when the red dye and indigo blue dye mixed together. The final color can also be due to the introduction of chromium into the mixture.
From there, the mineralogy of the pigment sample suggests that the dye was mixed with clay or a silica material to form a pigment. According to Butt, himself an established painter, pigments made in this way are called lake pigments (derived from the same root as the word lacquer). Additionally, the pigment was mixed with a beeswax binder before it was finally painted onto linden wood.
The pigment showed evidence suggesting a crystalline structure in the pigment. “The lake pigments were thought to be devoid of crystallinity prior to this work,” says Gates. “We now know that crystalline domains exist in lake pigments and these can work to ‘trap’ evidence of the environment during pigment creation.”
Bottom of the barrel, uh, tub
Another detail added a little more depth to the story of how this portrait was made. The researchers also found significant amounts of lead in the pigment and linked that discovery with the observations of a British explorer in the late 1800s who reported that the dyeing vats in Egyptian dyers’ workshops were made of lead.
“Over time, a story or a hypothesis has emerged,” says Butt, “suggesting that Egyptian dyers were producing red dye in these lead vats.” And by the time they’re done dyeing at the end of the day, he says, there may have been a purplish-colored sludge developing inside the tub. “Or they were very clever and might have found a way to take their red dye, shift the color to purple by adding a transition metal salt and a mordant. [a substance that fixes a dye] to intentionally synthesize a purple pigment. We do not know. “
Wider impacts
This isn’t the first time Butt has used scientific methods to learn about ancient works of art. He was involved in previous similar investigations and drew on both his research and his artistic background to develop a course called “The Science of Art” which included studies and discussions on topics that included dating, understanding and reverse engineering of a variety of artifacts. historians ranging from newspapers to pioneers of ancient art.
“Mixing science and art together is just fun,” he says. “It’s a great way to make science learning more accessible.”
And the work also has wider impacts. Relatively little is known about mummy portraits, including whether the same artist painted multiple portraits. Analyzing pigments at the atomic level could provide the chemical footprint needed to connect the portraits together.
“Our findings suggest a tool for documenting similarities regarding the time and place of production of the mummy portraits since most have been buried and have no archaeological context,” Gates says.
“So we might be able to connect families,” Butt adds. “We may be able to connect artists to each other.”
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