The earliest bronze artifacts found so far in China - a small knife and fragments of a small knife excavated from Gansu Province, northwest China - were produced during the period from 3,000 years BC to 2,300 years BC. Bits of copper articles were found from ruins of the Yangshao culture at Jiangzhai, Lintong City of Shaanxi Province, which are identified as dating back to around 4,700 years BC. Archeological findings suggest that the Chinese were producing bronze ware during the period of Longshan culture that came later, when stone tools were still used. Bronze, the alloy of copper and tin or lead, has a lower melting point than copper but it is harder. Bronze with a 10% copper content is 4.7 times as hard as copper. Melted bronze alloy expands a little in the course of cooling. For all this, bronze castings have fewer gas holes in them, suggesting that the alloy is good for casting.
Production of bronze ware was a complicated process. Before casting, there was the need to make a die in the shape of the object to be produced. The earliest bronze ware were produced mostly with a single mold and occasionally with two - the upper and the lower - for production of double-faced objects. More than two molds would be needed, including even internal molds, when things more complicated in structure were to be produced. Decorative designs and inscriptions were first carved on the molds, with which casting dies were made. Several dies had to be used to produce a bronze vessel with, indicating that the bronze casting technology was quite sophisticated.