TRACING MANUFACTURING TECHNIQUE IN AN ARCHAEOLOGICAL THIN SHEET TUBE FROM TEPE SAGZABAD IN QAZVIN PLAIN, IRAN (1500-800 BC)

Abstract

Recent excavations in Tepe Sagzabad in Qazvin Plain, Iran, yielded some archaeologi-
cal metal artifacts dating to the Early Iron Age. Among different metal fragments, a small
tube was found. As a part of systematic analytical research, thin sheet tube was studied
for elemental composition, manufacturing technique and deterioration mechanism using
optical microscopy (OM), scanning electron microscopy combined with energy disper-
sive X-ray spectroscopy (SEM-EDS) and Raman spectroscopy. The results of analyses
showed that the tube has been made from a thin sheet Cu-Sn alloy. In addition, it was
found that the tube was completely mineralized, and there was no sound metal remained
in it. Corrosion of the tube was composed of a bilayer structure in which the original
shape of the artifact has been preserved. Raman characterization of the corrosion prod-
ucts showed that the inner layer is composed mainly of cupric oxide (tenorite) beneath an
outer cuprous oxide layer (cuprite) which has grown outward from the original surface.
This is believed to be due to a corrosion phenomenon of bronze alloys known as "decu-
prification process". Moreover, microscopic investigation showed presence of elongated
inclusions merely in the inner layer indicating both the manufacturing process and the
limit of the original surface of the tube.