Exciting Pigments

Mar 25, 2014

Cinerary Urn with Reclining Man and Battle Scene, 2nd century BCE, Harvard Art Museums/Arthur M. Sackler Museum (after conservation).

A reclining figure rests atop an Etruscan cinerary urn (c. 200–150 BCE), while below him a bloody struggle is depicted. The warriors are thought to be Oedipus’s sons, who killed each other in their pursuit for kingship. With the exception of the reclining man’s dark pink face and arms, it appears at first glance that the urn is decorated only with a chalky white slip and clay-colored tones. But with the help of a simple, nondestructive technique called infrared luminescence imaging, the presence of a bright pigment known as Egyptian blue has been identified on this object.

Working with Susanne Ebbinghaus, George M. A. Hanfmann Curator of Ancient Art, Katherine Eremin, Patricia Cornwell Conservation Scientist, and Jens Stenger, Associate Conservation Scientist, from the Harvard Art Museums’ Straus Center for Conservation and Technical Studies have used this technique to identify and map the concentration of Egyptian blue pigment on a number of objects from the museums’ collections.

Conservation scientist Giovanni Verri from the British Museum has dated the first use of this important synthetic pigment to Egypt’s Fourth Dynasty (c. 2500 BCE). Over time, the bright blue pigment has flaked and largely disappeared from most objects. Fortunately, Egyptian blue is one of a select group of materials on which visible light is capable of inducing luminescence in the infrared spectral region (light that cannot be seen without special equipment). By simply removing the standard infrared-blocking filter on a digital camera, Stenger and Eremin were able to capture this otherwise invisible light with ease.

The infrared grayscale images have exposed a new picture of the urn: sections of the warriors’ armor glow bright white, the result of the Egyptian blue pigment emitting luminescence. Stenger described how the visible light excites the pigment’s electrons, causing the particles to shine strongly when recorded with the infrared-sensitive camera. This technique reveals trace amounts of Egyptian blue and can also be used to identify both Han blue and Han purple, two chemically related Asian pigments. “Infrared luminescence can help distinguish Egyptian blue from other blue pigments such as azurite or lapis lazuli, which were used at the same time and do not respond to this technique,” Stenger explained. “More important, the extremely high sensitivity of this technique helps answer the bigger question: was the object painted originally?”

“People have long struggled with the notion that ancient sculpture was painted,” said Ebbinghaus. “It’s an idea that hasn’t always been well received.” Take, for instance, D. Barrett Turner’s description of the urn, published in the 1933 Bulletin of the Fogg Art Museum. He details how “at one time gaudy colours painted in tempera on a white ground decorated this urn and enlivened the subject of death. Only traces of color can now be seen on the front relief, but the reclining man is lurid with purplish red flesh and black eyes and eyebrows.”

Most ancient sculptures were in fact painted. The Harvard Art Museums’ 2007 exhibition Gods in Color: Painted Sculpture of Classical Antiquity dispelled the notion that ancient sculptures were done in the white, unpainted marble that became the ideal for Renaissance sculptors. The exhibition presented color reconstructions of ancient Greek and Roman statuary based on close examination and scientific analysis of scarce traces of paint remaining on the surfaces of the original objects. This analysis was carried out with techniques similar to the one Stenger and Eremin recently used.

On the Etruscan urn, the concentration of Egyptian blue on the warriors’ helmets and breastplates not only delivers a more complete understanding of the object’s original appearance, it also confirms the use of iron armor in northern Italy in the 2nd century BCE; bronze armor would have been depicted in the metal’s characteristic golden-brown color. “Other materials from this same time period have not survived as well as terracotta; iron is one example,” said Ebbinghaus. Using infrared luminescence to survey the urn has “helped make ancient warfare come to life.”

  • The bottom part of the Etruscan urn depicting the battle scene, shown in natural light.
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    The bottom part of the Etruscan urn depicting the battle scene, shown in natural light.

  • Areas that glow white in this infrared luminescence image indicate the presence of Egyptian blue.
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    Areas that glow white in this infrared luminescence image indicate the presence of Egyptian blue.

  • Scientists Katherine Eremin and Jens Stenger use infrared luminescence imaging on other objects in the collections to identify the presence of Egyptian blue. Here they are looking at Cinerarium and Lid, 125–50 CE, Harvard Art Museums/Arthur M. Sackler Museum.
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    Scientists Katherine Eremin and Jens Stenger use infrared luminescence imaging on other objects in the collections to identify the presence of Egyptian blue. Here they are looking at Cinerarium and Lid, 125–50 CE, Harvard Art Museums/Arthur M. Sackler Museum.