A technological perspective on dynastic history

The two neighboring vassal states of Ba and Shu, which existed during the Eastern Zhou Dynasty (770-256 BC), had similar cultures. Located in what is today Chongqing and Sichuan province, they both became part of the Qin state in 316 BC, which paved the way for Emperor Qinshihuang to unify the country and establish the Qin Dynasty (221-206 BC).

For years, archaeologists have been studying that part of China's history from many angles, such as changes in the political system, the economic situation, handicrafts and cultural integration.

Some researchers specializing in archaeometry, scientific methods and technology used in archaeological study, are joining forces to enrich understanding from that perspective.

Researchers analyzed bronze yue axes and mou cooking vessels, two typical Shu artifacts unearthed at the Shuangyuan village site in Chengdu, Sichuan, and found the shape, original material and technique of making the two items changed after the Shu state became a part of Qin, said Luo Wugan, a professor at the University of Chinese Academy of Sciences in Beijing.

Tombs dating back to the Spring and Autumn Period (770-476 BC) and Warring States Period (475-221 BC) have also been found at the site, along with bronze vessels for daily use.

Typological analysis of the artifacts found they were mainly made in two periods, before and after Shu state became part of Qin. X-rays revealed the yue axes made earlier were thicker, had a smaller cavity, were made with more metal and functioned better. In the latter period they were thinner with a bigger cavity and had much less metal, Luo said.

Metallographic analysis suggested that after being cast, the vessels made earlier were hammered in some parts so they became harder, but later on the hammering was omitted.

Analysis of the materials showed the early-stage vessels were mainly made of bronze and tin, while those made later were composed of bronze, tin and lead.

"In the early stage the proportion of tin was high, reaching more than 10 percent. But in the later stage the proportion of tin decreased, and more lead was added to make them," Luo said.

By analyzing similar items from other locations, researchers excluded the possibility that the changes were influenced by neighboring areas.

Similar changes to the ratio of alloys used to make mou vessels were also found.

Luo said the proportion of tin declined while lead rose after the Shu people became part of the Qin.

Further examination of the production areas of the original materials through analysis of lead isotope ratios found that locally sourced copper and lead were mainly used to make some artifacts. However, the majority of copper and lead later used was transported from other areas.

"The change may be caused by Qin people's control over mine resources in the Shu area," Luo said.

"Through historical documents we know Qin people implemented a loose policy in the Shu area after it was integrated. As a result, they continued to produce Shu-style artifacts like bronze yue axes and mou, though done on the basis of controlling production, including the techniques and materials."