That's how I know that before the pre-Qin period, it was mostly knife coins. From the Qin Dynasty to the Jiajing period of the Ming Dynasty, bronze was used to cast money. During Jiajing period of Ming Dynasty, with the development of coinage technology, brass coins were used. Therefore, the copper coins that existed after Jiajing were all made of brass, and of course there were other materials, including copper. For example, the left uses the unique red copper in Xinjiang to cast coins.

Institutionally speaking, from the Qin dynasty to the early Tang dynasty, it was five baht, that is, half two. The Tang Dynasty abolished the five baht and cast Kaiyuan Bao Tong. Kaiyuan is the title of Xuanzong of the Tang Dynasty, so after Xuanzong of the Tang Dynasty, Kaiyuan Bao Tong was used, and Kaiyuan Bao Tong survived many times. Later, he didn't care about Yuan Dynasty, Ming Dynasty and Qing Dynasty. Most of them follow the standards of Kaiyuan Bao Tong. It's just that the words and patterns on the coins have changed.