Science reveals the secrets of the portrait of a mother

How much information can you get from a grain of purple pigment, no larger than the diameter of a hair, taken from an Egyptian portrait almost 2,000 years old? A lot, according to a new study. Analyzing this grain can tell us how the pigment was made, what it is made of – and maybe even a little bit about the people who made it. The study is published in the International Journal of Ceramic Engineering and Science.

“We’re very interested in understanding the meaning and origin of portraits, and finding ways to relate them and find a cultural understanding of why they were even painted in the first place,” says materials scientist Darryl Butt, study co-author 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 like what you might initially think of as a mummy – not like Tutankhamun’s golden sarcophagus, nor like the side paintings on the murals and papyri. Not like Boris Karloff either.

The portrait, called “Portrait of a bearded man”, comes from the second century, when Egypt was a Roman province, where the portraits are more realistic and less hieroglyphic than Egyptian art of previous eras. Most of these portraits come from an area called Faiyum, and there are around 1,100 of them. They are painted on wood and wrapped in the sheets that hold the mummified body. The portraits were meant to express the likeness of the person, but also their status – whether real or ambitious.

This idea of ​​status is actually very important in this case, as the man in the portrait we’re focusing on wears purple markings called The vinegar on his toga. “Since the purple pigment appeared in the clavi-the purple mark on the toga which in ancient Rome indicated a senatorial or equestrian rank – it was thought that perhaps we were seeing an increase in the importance of the model in the afterlife, ”says Glenn Gates of Walters Art Museum in Baltimore, where the portrait resides.

The color purple, says Butt, is considered 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 says that purple, located at the end of the visible color spectrum, can suggest the end of the known and the beginning of the unknown.

“The presence of purple on this portrait in particular made us wonder what it was made of and what it meant,” Butt says. “The color purple raises many questions.”

Lacquer pigments

Through a microscope, Gates saw that the pigment looked like crushed gems, containing particles ten to a hundred times the size of typical paint particles. To answer the question of how it was made, 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 track it.

“The particle was shipped to me from Baltimore, sandwiched between two glass slides,” Butt explains, “and since it had moved about a millimeter during transit, it took us two days to find it. . ” In order to move the particle to a sample holder, the team used an eyelash with a small amount of adhesive on its end to effect the transfer. “The process of analyzing something like this is a bit like doing surgery on a chip.”

With this particle, no matter how small, the researchers were able to machine even smaller samples using a focused ion beam and analyze those samples for their elemental composition.

What did they find? To put the results into context, you will need to know how dyes and pigments are made.

Pigments and dyes are not the same things. Colorants are the pure coloring agents and pigments are the combination of colorants, 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 hypothesize that the purple used in this mummy painting is something else – a synthetic purple.

The researchers also hypothesize that synthetic violet could have 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 in the mixture.

From this, the mineralogy of the pigment sample suggests that the dye was mixed with clay or silica material to form a pigment. According to Butt, an accomplished painter himself, the pigments made in this way are called lacustrine pigments (derived from the same root word as lacquer). Additionally, the pigment was mixed with a beeswax binder before it was finally painted onto linden wood.

The pigment has shown evidence suggesting a crystal structure in the pigment. “The lacquer pigments were thought to be crystal-free prior to this job,” says Gates. “We now know that crystalline domains exist in pigment lakes, and these can function to ‘trap’ environmental evidence during pigment creation.

Bottom of the barrel, uh, tank

Another detail added a little more depth to the story of the making of this portrait. The researchers also found significant amounts of lead in the pigment and linked this discovery to observations of a British explorer in the late 1800s who reported that dye vats in Egyptian dyers’ shops were made of lead.

“Over time, a story or hypothesis emerged,” Butt says, “suggesting that Egyptian dyers were producing red dye in these lead vats.” And when they were done dyeing at the end of the day, he said, there may have been a slime that developed inside the tub that was a purplish color. “Or they were very smart and maybe they found a way to take their red dye, change the color to purple by adding a salt with some transition metals and a biting. [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 more about ancient works of art. He was involved in previous similar investigations and relied on both his research and his artistic background to develop a class called “The Science of Art” which included studies and discussions on topics involving dating. , understanding and reverse engineering a variety of historical artifacts ranging from pioneering journals to ancient art.

“Mixing science and art is just plain fun,” he says. “It’s a great way to make science learning more accessible.”

And work also has wider impacts. Relatively little is known about the portraits of mummies, especially if the same artist painted multiple portraits. Analysis of pigments at the atomic level can provide the chemical fingerprint needed to connect the portraits to each other.

“Our results suggest a tool for documenting similarities regarding the time and place of production of the mummy portraits, as most were stolen from graves and lack archaeological context,” Gates says.

“So maybe we can connect the families,” Butt adds. “We might be able to connect artists to each other.”