Modern Machine Solves Old Mystery: Metal “Fingerprint” Reveals Genuine Artifact

Innovative 21st century technology recently transported scientists and historians back to the 16th century in a search for truth. Argonne’s Advanced Photon Source (APS) is able to reveal an object’s composition, crystal structure and thickness without damaging the object.

The APS was used to study two astrolabes, instruments that were used to tell time through the positions of the stars before the telescope was invented. These two instruments were from different collections, Chicago’s Adler Planetarium and Harvard University, but each bore the same name, “Ioannes Bos,” and date “24 March 1597.” It is unlikely that the same craftsman would have completed two such instruments on the same date.

“Museum curators need to know which astrolabes are genuine, so they aren’t deceived by reproductions,” says Bruce Stephenson, director of the history of astronomy department at the Adler Planetarium and Astronomy Museum in Chicago. Stephenson’s brother Brian works in Argonne National Laboratory’s Materials Science Division and suggested they use the laboratory’s APS to solve the mystery scientifically.

The Stephenson brothers were joined by Dean Haeffner of Argonne’s APS. “In this experiment, we were able to merge history with our knowledge of materials science,” Haeffner explains.

The astrolabes were studied at the Synchrotron Radiation Instrumentation Collaborative Access Team beamline.

Fluorescence analysis was used to determine the element composition. X-rays emitted from the test have a characteristic spectrum, or “fingerprint,” which reveals each element present and its quantity. X-ray fluorescence revealed the Adler astrolabe to be made of a copper-zinc alloy with silver, tin, lead, nickel and antimony impurities; it is “old brass.” The Harvard astrolabe, however, has no zinc and is gold-plated copper. In addition to gold, it contains mercury and silver from the gilding process.

Diffraction analysis was used to determine the crystalline texture of the astrolabes. The deflected X-rays are concentrated in certain directions, and recorded as a diffraction pattern. The diffraction pattern from the plate of the Adler astrolabe displays a random orientation of fine crystals in the metal, indicating that the plate was hand-hammered. The Harvard plate had a strong directional pattern of crystal orientations with identical texture in different areas of the plate. This indicates that the plate was made of rolled metal, a technique not available for plates this large in 1597.

Radiography was used to study the thickness of each plate of the astrolabes. By scanning the sample through an X-ray beam and recording the intensity of the X-rays that are transmitted, researchers created a thickness profile. The Adler astrolabe has irregular thickness variations consistent with hand hammering; the Harvard astrolabe has the uniform thickness of a rolled plate.

The researchers concluded that the composition of the Adler astrolabe is consistent with technology of 1597. The Harvard instrument, however, reveals a more recent technology.

“Perhaps a materials scientist may be too focused on reproducible general phenomena, to the neglect of individual variations,” Bruce Stephenson says. “And the historian may focus on particular details and fail to see beyond them.” The researchers agree that scientists and historians can profit from exposure to each other’s point of view.

For more information please contact Catherine Foster at 630-252-5580

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