Why is the "Duguxin Polyhedral Coal Seal" the oldest seal in China?

Duguxin polyhedral coal seal is a cultural relic of the Western Wei Dynasty, which was unearthed in Xunyang County, Shaanxi Province 198 1. It is 4.5 cm high and 4.35 cm wide. Duguyinxin is a seal made of coal concentrate. This seal is a polyhedron composed of 26 squares and triangles of different sizes, of which 14 squares are engraved with standard regular script. Now it is collected in Shaanxi History Museum.

The material and shape of Dugu seal are special, and the seal with multi-face seal is unique in the history of China seal, so it is called "a rare national treasure".

The seal is made of fine coal and is spherical, with 8 edges and 26 faces, of which 18 square faces and 8 triangular faces. There are 14 square seals, namely "Official Letter on Sparse", "Official Letter on Seal", "Official Letter on Form", "Official Seal", "Official Seal", "Secretariat Seal", "Official Letter on White Book" and "Official Letter on White Note". The seal is regular script, the calligraphy is tall and straight, and I have a strong interest in Shu Wei. According to the content of the seal and the textual research of historical books, this seal is Du Zhiyin, a fu writer in the Northern Zhou Dynasty. Fourteen seals have different contents and uses, and are valuable physical materials for studying the seal system of the Northern Dynasties.