Ancient Pigment Egyptian Blue May Find New Life as Nanotechnology

by Meg Marquardt

Materials Research Society | Published: 06 March 2013

egyptian-blue-200 A sample of exfoliated Egyptian blue pigment. Image credit: Tina Salguero. Click image to enlarge.

Egyptian blue (CaCuSi4O10) is considered the world’s first artificial pigment: its composition recipe was described in texts from the third millennium B.C. as a mix of sand, salts and copper. Now, new research published in the Journal of the American Chemical Society may bring Egyptian blue into the 21st century. With sought after near-infrared radiation emission and a remarkably simple creation process, CaCuSi4O10 may be the next big thing in nanotechnology. 
Tina Salguero, a professor of chemistry at the University of Georgia, leads nanosheet research for new technological applications. Often, she says, nanosheets are made from layered materials. Through various processes, the layers can be disassembled, producing nanosheets that are sometimes thinner than one nanometer. It was natural, she says, to look at Egyptian blue, a material well known for being composed of layers. 

Egyptian blue stood out as a possible nanosheet candidate for another reason. The material’s copper component emits near-infrared radiation. Other materials also emit near-IR, but they are commonly based on rare earth elements, materials that are expensive and currently in short supply. CaCuSi4O10, by contrast, is made of fairly common elements that could easily be produced in bulk, says Salguero. 

Identifying how to exfoliate the material seemed like it would be a mighty task from the outset.  Egyptian blue has maintained its brilliant hue in artwork that has lasted millennia. The pigment even survived major natural disasters, with large quantities found at the ruins of Pompeii. It came as a shock, then, says Salguero, when they discovered a simple method that disassembled the layers: stirring in hot water. 

“Initially we were trying with much more sophisticated chemistries,” she says. “It was only when my graduate student, Darrah [Johnson-McDaniel], did the control experiment that we found that just water worked.” 

When Johnson-McDaniel, the first author on the paper, stirred CaCuSi4O10 in water at temperatures of at least 80°C, the materialdelaminatedinto nanosheets thinner than 10 nanometers. Cooler water temperatures, those less than 40°C, also caused some delamination, though at a much slower rate. The reduced rate may explain why Egyptian blue remained damaged but intact on surfaces that would have seen environmental moisture. 

“Recognition of the nanosheet delamination perhaps has impact on our understanding of the appearance of some examples that may not retain their color on either a macro or micro scale,” says Renee Stein, a conservator at the Michael C. Carlos Museum at Emory University, who is unaffiliated with the current research. “Sometimes a painted surface will look quite colored, but viewed microscopically, the [top] layer may be somewhat discolored…If and when discoloration is observed it could possibly be explained by the formation of nanosheets.” 

The nanosheets maintained the near-IR emitting properties of the starting bulk material, says Salguero, meaning Egyptian blue could find new life in many applications, including security ink and more powerful biomedical imaging.   

Read the abstract in the Journal of the American Chemical Society here.

 


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