Left, an ivory carving from Arslan Tash is scanned by the SLcam. On the right, a possible reconstruction of the gold originally gilded onto the surface.
Credit: the Laboratoire d’Archéologie Moléculaire et Structurale, University of Paris
Ancient cities were not the pale mausoleums that we see today. Researchers have long believed that the faded ivory, marble and stone remnants of the ancient world were once brightly painted and gilded.
Such theories were difficult to prove, however. Microscopes such as the scanning electron microscope, or SEM, require that users take a microsample of the object being observed and place it on a slide. This is not ideal for art pieces and other historical objects, where the main goal is preservation.
But now, a team of researchers have developed a new, highly effective and noninvasive procedure for viewing trace materials on the surface of ancient objects.
Called the SLcam, the device uses unfocused X-ray beams to make the trace elements on the object's surface fluoresce, or glow. Then a camera with microscopic spatial resolution— nearly 70,000 pixels —captures color images of the X-ray fluorescence lines, which are then analyzed to determine the identity of the elements. The SLcam also uses a technology called polycapillary optics that allows it to capture the depth and contours of these three-dimensional carved objects. [See also: New Camera Sensor Eliminates Need for Flash]
Lead by Ina Reiche, a researcher at the Laboratoire d’Archéologie Moléculaire et Structurale at the University Pierre and Marie Curie Paris 6, the researchers used this new technique to analyze a series of 2,800-year-old ivory carvings from Arslan Tash, a city in the ancient Mediterranean kingdom of Phoenicia that is now part of Syria.
In the past, the technique of using X-ray fluorescence had been applied to individual objects. But this study marks the first systematic use of a cutting-edge X-ray fluorescence detection device like the SLcam.
The SLcam is not without limits: It can only tell what basic elements are on the ivory's surface, such as copper, lead or gold. From there, the researchers have to take what they know of Phoenician society and make a few inductions.
For example, the carvings were done in an Egyptian style, and researchers know that Egyptians used copper to create blue and green paints, and lead to create reds. So when researchers find copper on the artifacts' surface, it's a good bet that those areas were at one point painted blue or green.
Using this knowledge, Reiche and her team mapped the distribution of trace elements across dozens of ivories in the collection, and are now using the maps to recreate the ivories' original Phoenician look.
Part of the challenge is determining which elements were from the paint and décor and which were simply the consequence of being buried for 2,000 years.
The researchers observed no radiation damage or other long-term effects from their study. Even though collagen, a fibrous protein found in the bones, ligaments and marrow of mammals, is highly vulnerable to radiation, most of the collagen in the ancient ivory had already degraded. The remaining bone comprising the ivory was unaffected by the X-rays.
The excavation took place in 1928, at a time where, as Reiche explains, archaeological digs tended to become something of a "free-for-all."
For example, the wooden furniture that these ivory carvings once adorned was excavated in such a way that caused it to degrade almost instantly.
The pieces uncovered at Arslan Tash were scattered across the globe. Many are now in museums, but it's likely that a significant number still reside in private collections.
Digital technologies could help reunite the scattered artifacts of Arslan Tash, allowing for a more cohesive study of ancient Phoenician art. [See also: How a Computer Model Could Help Fight Terrorism]
According to research by Giorgio Affanni, a professor of anthropology at the University of Torino in Italy, more than 200 of these ivory carvings were excavated and are now housed in collections across the world, including the Louvre in Paris and museums in New York, Hamburg, Aleppo and Jerusalem.
Reiche and her team now hope to create 3D models of the artifacts that display them with their original color. Eventually, these models could be used to approximate the appearance of the original furniture, including the long-since-disintegrated wood.
This study, published in the journal Analytical Chemistry, comprised 84 ivory pieces from the Louvre and the Badisches Landesmuseum in Karlsruhe, Germany, selected together with Elisabeth Fontan, curator in chief at the Louvre's Departement des Antiquités Orientales.