Chinese Bronze Bowl
A ritual bronze vessel in the Krannert Art Museum dates stylistically to the late 10th century B.C., or Middle Western Zhou Period. Curators requested materials analysis to confirm whether or not the metal composition and the manufacturing technique were consistent with the early date.
A pinpoint analysis of metal from the underside of the bowl by scanning electron microscopy with an energy-dispersive X-ray attachment showed only three elements with a concentration greater than about 0.1%: copper (80%); tin (15%); and lead (2%). This composition of a copper-tin bronze with a little lead added as a flux is consistent with that of other Chinese bronze vessels in the 10th century B.C.
Next, the bowl was subjected to X-ray radiography to examine its internal structure. The X-rays showed porosity in the metal (seen as black dots against a grey background) typical of early casting technology when bubbles of gas were trapped. Chaplets (spacers between the mold and core), slots for the escape of gases, and the stump of a sprue (duct for pouring the molten metal) revealed on the underside indicate that the vessel was cast upside-down, probably in a single pouring operation using a sectional mold.
The combined analytical data confirmed the stylistic assessment of this vessel as an authentic Chinese bronze of the Middle Western Zhou period.
For a fuller description, see the "Insights" exhibition catalogue.