Using characterization techniques for determining the history of a 2 millennia old kettle made of bronze alloyed with iron

Abstract

A bronze kettle dating from the 1st to 2nd Century was found in a riverbed of the Kupa river in Croatia. After excavation it spent another 50 years in a depot of a museum in atmospheric conditions prior to starting the conservation treatment and our studies. A study on the surface layers development was performed to determine the history of the object. This study is a demonstration of how such analysis can be used to reconstruct what the object went through during its life span.It was determined that the kettle is made of low-tin bronze, called mild bronze, with addition of iron, aluminum, calcium and nickel. Using iron for alloying copper is unusual since pure iron is generally not added to bronze, thus the presented case is a rare subject. Presence of cassiterite SnO2 showed that the kettle was used for preparing food on open fire prior to ending up in the river. While being in the riverbed malachite formed on the kettle. After longer exposure to the river Si-oxides and CaCO3 formed on the surface of the kettle, over malachite. It was shown that the kettle probably had a ferrous alloy handle which degraded and disappeared in time. After excavation, the kettle came again in an oxygen-enriched atmosphere and developed additional surface layers over the malachite layer.