Bronze Age Artifacts

Bronze age artifacts, physical links between us and people alive 3000 years ago, have long been closely examined with physics-based instruments such as x-ray crystallography and mass spectrometry.

Now scrutiny of microchemical surface properties of such ancient bronze in some respects surpasses the diagnostic information gained by previous bulk-phase studies. Ernesto Paparazzo of the Instituto di Stuttura della Materia in Rome (paparazzo@ism.rm.cnr.it, 39-06-4993-4153), and his colleagues at the Pacific Northwest National Lab and Oxford, have looked at an early-first-millennium BCE belt from Syria with scanning auger microscopy (SAM), a process in which specific elements in a material can be identified when electrons with characteristic energies are knocked out of atoms by an incoming electron beam.

Bronze is an alloy of copper and tin---generally a mixture of about 85% copper and 10% tin, with minor amounts of other metals being also possible (e.g., zinc, lead, etc.). Metals put back into the earth naturally rust but unequally, leading in the case of bronze to "decuprification," that is, the disproportionate detachment of copper atoms from the bronze.

With their SAM device, the researchers have studied this process, and have characterized the microchemistry of the bronze at a level of spatial resolution as good as 15 nm, the best yet achieved for the analytical study of an archeomaterial. They can inventory the invasion of silicates into the alloy from surrounding soil during the burial phase and even spot alloy inhomogeneities introduced by the smith during the manufacturing phase. (Paparazzo et al., Journal of Vacuum Science and Technology A, July 2001.)