Historically, the materials used in production tools have been continuously improved. It has a close relationship with the development of human society. Therefore, historians used the material of artifacts to mark historical periods, such as the Stone Age, the Bronze Age, and the Iron Age. By the end of the 17th century, eight kinds of non-ferrous metals were clearly recognized and applied by humans. The Chinese nation has made significant contributions to the discovery and production of these non-ferrous metals (see Metallurgical History). After entering the 18th century, the rapid development of science and technology has promoted the discovery of many new non-ferrous metal elements. In addition to the eight types of non-ferrous metals mentioned above that were recognized and applied before the 17th century, 13 were found in the 18th century. In the 19th century, 39 species were discovered. In the 20th century, 4 species were discovered.