When a woman lost a small tin of face cream in 2nd-century London, she probably didn't think of posterity. Twenty-first century archaeologists are grateful for her negligence. The newly discovered tin is the first personal care product of the Roman Empire to come down to us with its contents intact.
The chemists analyzing those contents call the discovery "a landmark in the study of this class of artifact." Their research at Britain's University of Bristol exemplifies the new science of archaeochemistry.
Chemists always have put their skills at the service of archaeology. But powerful analytical techniques that evolved over the past few decades have raised their work to the level of a distinct archaeological science. Archaeochemists sift through molecules to find clues to ancient lifestyles as skillfully as traditional archaeologists sift through sand.
Take Kathryn Jakes, a professor of consumer sciences at Ohio State University in Columbus who is studying archaeological textile fragments. For her, sifting through the composition of fibers left by the Hopewell and Mississippi cultures of ancient North America is an exploration into everyday parts of personal lives.
"Knowing the chemical and physical composition of such pieces is significant because even small remnants give us fascinating clues," she says. "We can even discern how the fabrics were worn and we can propose what they were used for."
Her work is like learning about someone's personality, Professor Jakes adds. "It's like getting in touch with somebody else's soul."
Archaeochemist Richard Evershed at the University of Bristol and his colleagues pursue this quest through the very personal medium of cosmetics. They explained in a recent issue of Nature how their analysis of the Roman face cream enabled them to recreate a product that might make Estée Lauder proud.
Studies of how bits of the cream dissolve in various solvents revealed fatty acids that indicate an animal origin for key ingredients. Running samples through systems that identify individual molecule types showed the presence of starch - an ingredient still used in cosmetics.
X-ray probing revealed the white pigment in the cream contained an oxide of tin. This is significant. Romans' favorite white pigment was lead oxide. The Bristol team points out that the substitution of tin for lead was made after Romans became aware of the toxicity of lead. Tin was a safe substitute conveniently available from mines in nearby Cornwall, England.
The analyses show that the creammakers had a sophisticated technology. Many tin compounds are toxic. They used an oxide of tin that is safe. It's readily prepared by heating refined tin metal in the air, according to the Bristol team.
The creammakers also heat-treated their animal fat and extracted starch from roots and grains with boiling water.
The researchers then mixed up a batch of the cream, using the ingredients they had identified in what they consider to be the correct proportions.
"The cream had a pleasant texture when rubbed into the skin. Although it felt greasy initially, owing to the fat melting as a result of body heat, this was quickly overtaken by the smooth powdery texture created by the starch," they report.