(A)
“Portrait of a Bearded Man†(Walters Art Museum #32.6), dated c. 170-180 CE
from Roman Imperial Egypt; (B) The portrait under ultraviolet light. The purple
clavi on the shoulders appear pink-orange, indicated by an arrow. Courtesy: The
Walters Art Museum.
Scientific
analysis of an ancient portrait pigment reveals long-lost artistic details.
How much
information can you get from a speck of purple pigment, no bigger than the
diameter of a hair, plucked from an Egyptian portrait that’s nearly 2,000 years
old? Plenty, according to a new study. Analysis of that speck can teach us
about 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 the International Journal of
Ceramic Engineering and Science.
“We’re
very interested in understanding the meaning and origin of the portraits, and
finding ways to connect them and come up with a cultural understanding of why
they were even 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 came from an Egyptian mummy, but it
doesn’t look the same as what you might initially think of as a mummy—not like
the golden sarcophagus of Tutankhamen, nor like the sideways-facing paintings
on 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, hence the portraits are more lifelike and less
hieroglyphic-like than Egyptian art of previous eras. Most of these portraits
come from a region called Faiyum, and around 1,100 are known to exist. They’re
painted on wood and were wrapped into the linens that held the mummified body.
The portraits were meant to express the likeness of the person, but also their
status—either actual or aspirational.
That idea
of status is actually very important in this case because the man in the
portrait we’re focusing on is wearing purple marks called clavi on his toga.
“Since the purple pigment occurred in the clavi—the purple mark on the toga
that in Ancient Rome indicated senatorial or equestrian rank- it was thought
that perhaps we were seeing an augmentation of the sitter’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 viewed 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 the 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.
“So the
presence of purple on this particular portrait made us wonder what it was made
of and what it meant,†Butt says. “The color purple stimulates many questions.â€
Lake
pigments
Through a microscope, Gates saw that the pigment looked like crushed gems, containing particles ten to a hundred times larger than 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 keeping track of it challenging.
A
magnified detail of the left clavus, showing a large purple pigment particle
with a rough gem-like appearance. Courtesy: University of Utah.
“The
particle was shipped to me from Baltimore, sandwiched between two glass
slides,†Butt says, “and because it had moved approximately a millimeter during
transit, it took us two days to find it.â€
In order to move the particle to a specimen holder, the team used an
eyelash with a tiny quantity of adhesive at its tip to make the transfer. “The
process of analyzing something like this is a bit like doing surgery on a
flea.â€
With that
particle, as small as it was, the researchers could 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 in context, you’ll need to know how dyes and
pigments are made.
Pigments
and dyes are not the same things. 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,
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 the synthetic purple could have originally
been discovered by accident when red dye and blue indigo dye mixed together.
The final color may also be due to the introduction of chromium into the mix.
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, an accomplished painter himself, pigments made in this way are called lake pigments (derived from the same root word as lacquer). Further, the pigment was mixed with a beeswax binder before finally being painted on linden wood.
A
pigment sample showing layering within the particle. Courtesy: University of Utah.
The
pigment showed evidence suggesting a crystal structure in the pigment. “Lake
pigments were thought to be without crystallinity prior to this work,†Gates
says. “We now know crystalline domains exist in lake pigments, and these can
function to ‘trap’ evidence of the environment during pigment creation.â€
Bottom of
the barrel, er, vat
One other
detail added a bit more depth to the story of how this portrait was made. The
researchers found significant amounts of lead in the pigment as well and
connected that finding with observations from a late 1800s British explorer who
reported that the vats of dye in Egyptian dyers’ workshops were made of lead.
“Over
time, a story or hypothesis emerged,†Butt says, “suggesting that the Egyptian
dyers produced red dye in these lead vats.†And when they were done dyeing at
the end of the day, he says, there may have been a sludge that developed inside
the vat that was a purplish color. “Or, they were very smart and they may have
found a way to take their red dye, shift the color toward purple by adding a
salt with transition metals and a mordant [a substance that fixes a dye] to
intentionally synthesize a purple pigment.
We don’t know.â€
Broader
impacts
This isn’t
Butt’s first time using scientific methods to learn about ancient artwork. He’s
been involved with previous similar investigations and has drawn on both his
research and artistic backgrounds to develop a class called “The Science of
Art†that included studies and discussions on topics that involved dating,
understanding and reverse engineering a variety of historical artifacts ranging
from pioneer newspapers to ancient art.
“Mixing
science and art together is just fun,†he says. “It’s a great way to make
learning science more accessible.â€
And the
work has broader impacts as well. Relatively little is known about the mummy
portraits, including whether the same artist painted multiple portraits.
Analyzing pigments on an atomic level might provide the chemical fingerprint
needed to link portraits to each other.
“Our
results suggest one tool for documenting similarities regarding time and place
of production of mummy portraits since most were grave-robbed and lack
archaeological context,†Gates says.
“So we
might be able to connect families,†Butt adds. “We might be able to connect
artists to one another.â€