Making Color

Scholars have long known that Egyptian blue pigment, the world’s oldest synthetic pigment, was a highly prized commodity in ancient times.  

Existing in ancient Egypt about 5,000 years ago, it was used in place of expensive minerals like turquoise or lapis lazuli and was used to paint wood, stone, and a papier-mâché-type material called cartonnage.  

Still, there has always been limited archaeological evidence of how Egyptian blue was produced. The Romans used the pigment after the Egyptians but by the Renaissance period, the knowledge on how to make it was mostly lost – until now. 

“It started out just as something that was fun to do because they asked us to produce some materials to put on display at the museum,” said lead study author John McCloy, part of a team that managed to recreate the color, in a statement. “But there’s a lot of interest in the material.”  

To study the composition of the pigment, the researchers created 12 different recipes from mixtures of silicon dioxide, copper, calcium, and sodium carbonate. They then heated the material at approximately 1830 degrees Fahrenheit for between one and 11 hours to replicate the temperatures they think would have been accessible for Egyptian artists. 

They then cooled the samples at different rates and studied the pigments using modern microscopy and analysis techniques never before used in this type of research.  

They compared their results with ancient Egyptian artifacts from the Carnegie Museum, which, along with the Smithsonian’s Museum Conservation Institute, collaborated on the study. 

Egyptian blue came in a range of shades, varying based on the production location and quality. Depending on the ingredients used and the processing time, the color could range from deep blue to dull gray or green. The study showed that the pigment is very diverse in composition. 

“You had some people who were making the pigment and then transporting it, and then the final use was somewhere else,” said McCloy. “With just small differences in the process, you got very different results.” 

Surprisingly, they found that to obtain even the bluest color, only about 50 percent of the blue-colored components are needed. 

“It doesn’t matter what the rest of it is, which was really quite surprising to us,” said McCloy. “You can see that every single pigment particle has a bunch of stuff in it – it’s not uniform by any means.” 

Researchers say the study results could help in the restoration of ancient artifacts that used this prized pigment.  

Also, there is interest in how to produce this pigment because of its optical, magnetic, and biological properties, and its potential for new technological applications.  

That’s because the pigment emits light in the near-infrared part of the electromagnetic spectrum – which the human eye can’t see – so it could be used for counterfeit-proof ink, for example. It also shares chemical similarities with high-temperature superconductors.