The invention of metallurgy is a revolutionary event in the history of human kind. Copper and iron were the two major metals in the early stage of metallurgy. The wide application of bronze and iron tools had played an important role in the development of ancient societies. Hence archaeologists name the stages after the Stone Age in the prehistoric time Bronze Age and Iron Age, and the origin of bronze and iron has long been heated topic in archaeology.
Research on the origin of metallurgy in China can be traced back to the beginning of the 20th century. Record in ancient texts was almost the only data at that time. After the 1920s, as modern archaeology emerged and developed in China, archaeological data became the new base for the research. By combining archaeological discoveries and ancient record, scholars found an effective way to explore early metallurgy in China, and had been continually making noticeable progress after the 1950s.
Copper works earlier than the 16th century BC have been unearthed in four regions within China. 1) The Northwestern Region including Gansu, Qinghai and the eastern Xinjiang. A small bronze knife found at the Linjia site, Dongxiang, Gansu dating to 3000 BC is the earliest metal object of this region. 2) The Northern Region including the central and southern Inner Mongolia, the western Liaoning and the southern and northern areas of Mt. Yanshan. Copper objects of this region can be dated from the 20th century BC to the 16th century BC. 3) The Haidai Region including the eartern Henan and Shandong. The earliest metal object of this region is a brass awl from the Sanlihe site, Jiaoxian, Shandong dating to 2400 BC. 4) The Central Plains Region including the eastern Guanzhong (central Shaanxi), the western Henan and the southern Shanxi. Except for a few brass objects which might be as early as around 4500 BC, most of the copper objects of this region can be dated from the 21st century BC to the 16th century BC. From the archaeological perspective, early copper objects of the Northwestern Region and the Northern Region might belong to one cultural system, while those of the Haidai Region and the Central Plains Region might belong to another cultural system. Hence I suggest a double-centers model of the origin of bronzes in China. The developmental process of bronzes in the Central Plains Region consists of three stages: the initial stage from 4500 BC to 2500 BC, the developing stage from 2500 BC to 2000 BC and the mature stage from 2000 BC to 1600 BC.
More than 140 iron objects earlier than the 5th century BC have been found in 39 sites within China. Except for several meteoric iron objects, all of them are man-made iron objects. Two systems of early iron objects can be archaeologically recognized in China. One is the Northwestern System represented by the iron works found in Xinjiang and adjacent areas. The earliest iron objects of the system emerged not later than the 10th century BC. The small iron knife discovered in the Yanbulake cemetery might be even can be dated to the 13th century BC. The other is the Central Plains System represented by the iron works found within the conjunctive area of Henan, Shaanxi and Shanxi. The iron ge dagger, the sword and the spear unearthed form the cemetery of the Guo State in Sanmenxia, Henan can be dated to around 800 BC. According to the metallographical analysis, the earliest iron objects in the Central Plains area were made of wrought iron or cemented steel from wrought iron. Most of them are part of a bronze-iron combination object. Pig iron smelting and founding techniques emerged around the 7th century BC. Tools completely made of iron, such as the cha fork, the spade and the knife, appeared around the 6th century BC. The middle of the 5th century BC witnessed the appearance of the decarbonized cast iron, the malleable cast iron and the decarbonized steel, as well as steel swords and casting iron vessels.
The application of bronze and iron tools had greatly promoted the development of ancient societies. The emergence of bronzes in the Central Plains had been one of the crucial factors of the origin of early states in that area. The development of iron casting techniques had played an important role in the social-economic changes during the Warring States period which leaded to the formation of the Qin and Han Empires.