MCI Researchers Help Recreate the World’s Oldest Pigment

Researchers at the Smithsonian’s Museum Conservation Institute have solved the mystery of “Egyptian Blue.”

Imagine walking down the street and seeing a beautiful chocolate cake in the window. Simple and elegant, it’s ganache coating glistening in the morning sun. The cake would be perfect for your nephew’s birthday party that evening, as he loves chocolate. But as luck would have it, it’s also a holiday and the bakery is closed. You have no choice but to recreate the cake at home.

You go to the grocery store and buy flour, sugar, eggs, and all the other ingredients you need for your cake. But then you realize that without a recipe, it’s not so easy to recreate the cake from the bakery. In what proportion do you add the different ingredients? What temperature do you set the oven to, and how long do you bake the cake for? If only you could analyze the cake from the bakery to identify the ingredients and how it was made.

If you worked at the Smithsonian’s Museum Conservation Institute, you would have some tools in your laboratory that could help you with this task. This is precisely what MCI did in a recent investigation, but their goal wasn’t to bake a cake; rather it was to recreate the world’s oldest pigment: Egyptian blue, which was used in ancient Egypt about 5,000 years ago.

An example of Egyptian blue pigment used on an ancient artifact. (Photo courtesy Washington State University)

“It started out just as something that was fun to do because [the Carnegie Museum of Natural History in Pittsburgh] asked us to produce some materials to put on display…but there’s a lot of interest in the material,” said John McCloy, co-first author of the paper and director of Washington State University’s School of Mechanical and Materials Engineering.

Engineers are interested in the pigment because it has unique properties with potential in new technologies. For example, the pigment emits infrared light, which could make it useful for applications like counterfeit-proof inks.

McCloy and an interdisciplinary group of scientists began analyzing the chemical properties of ancient Egyptian blue samples, hoping to identify how it was made. Undergraduate student Julia Esakoff ran some experiments and conducted some basic characterization of the experimental material.

Egyptian blue pigment can be seen on this painted artifact. (Photo courtesy Washington State University)

At that point, McCloy realized there was more to figure out if they wanted to successfully recreate the pigment, so he contacted Ed Vicenzi and Thomas Lam at MCI to add their insights. “John was aware that Thomas and I had recently correlated color and composition at the microscopic scale in work conducted with Susan Smith at the National Postal Museum,” said Vicenzi. “The initial results were fascinating, as we encountered different issues that impact the pigment’s color. With time, the Smithsonian’s role in the project grew larger until John asked me to join him as co-lead author on the paper.”

Egyptian blue pigment can be seen on tis artifact. Courtesy WSU

Ed’s and Thomas’ work focused on measuring the quantitative color of the pigment and its components (in the analogy above, that would be the taste and ingredients of our cake, respectively). They also analyzed the composition of various experimental and commercial reference materials as the team sought to recreate Egyptian blue.

Close-up of a researcher taking a pigment sample from a small wooden falcon. (Photo courtesy Matt Unger, Carnegie Museum of Natural History)

To understand its makeup, the research team ultimately created 12 different recipes of the pigment from mixtures of silicon dioxide, three different copper sources, calcium carbonate, with or without sodium carbonate. They heated the material at about 1000 degrees Celsius (about 1830 degrees Fahrenheit) for between one and 11 hours to replicate temperatures that would have been available for ancient artists. After cooling the samples at various rates, MCI studied the pigments using modern microscopy and analysis techniques. Ed and Thomas’ efforts to characterize the color of such a wide variety of Egyptian blue materials in detail, together with the other analytical and imaging techniques used by the team, represent a combination of methods previously unused for this type of research; comparing pigments created in the laboratory to fragments from ancient Egyptian artifacts.

Samples of the Egyptian blue pigment used on ancient artifacts. (Photo courtesy Washington State University)

Ed and Thomas’ analysis will help McCloy and other scholars establish a modern recipe for Egyptian blue, which will inform its production and use in a wide variety of applications, from fingerprint detection to solar energy generation.

“In summary, the work Thomas and I performed dovetailed beautifully with WSU’s data,” said Ed. “We feel the work conducted at the Smithsonian could open up new possibilities for other discoveries in heritage, as well as natural sciences.”