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Mesopotamia's true colors
Using a scanning electron microscope (SEM), conservators at the Oriental Institute (OI) correctly reidentified the pigments on this mud-brick wall fragment (at right). From Khorsabad, Iraq, the capital city of Assyrian King Sargon II (721-705 B.C.), the 6 x 10 cm fragment was probably part of a geometric painting that graced the palace walls (see reconstructions below). In storage since the 1930s, the fragile piece needed strengthening treatment before the OI Mesopotamian Gallery opens in fall 2003.

Before using modern materials during the treatment, the conservators needed to analyze the pigments. Although OI publications from the 1930s said mercuric sulfide was used for the red color and lapis lazuli (a sulfur containing sodium aluminum silicate) for the blue, the conservators were skeptical: those pigments were rarely used by Sargon's time.

For a closer look, OI researcher Vanessa Muros used the geophysical-sciences department's SEM, which provides high-resolution, highly magnified images and identifies the presence and proportion of elements. The scan revealed iron, not mercury, in the red pigment, indicating an oft-used iron-oxide-based material. The blue dye contained copper, silica, and calcium—not sodium—and was probably "Egyptian Blue," commonly used in antiquity.

The scan offered reassurance that a diluted resin wouldn't harm the fragment. It also showed, then-OI Museum Director Karen Wilson says, that the Assyrians "were using a more elaborate process of manufacturing pigments than we previously thought."

— A.B.