The extended information stamp is used as letterhead printed on a document to indicate identity or signature. Generally, seals are dyed with pigments before printing. Those that are not stained with pigment and will appear concave and convex after being printed on a flat surface are called steel seals, and some are wax prints printed on wax or wax paint or envelopes. Made of metal, wood, stone, jade, etc.
As a work of art, the value of seal is generally manifested in two aspects. One is its shape design, that is, the design of printed buttons, casting skills and later higher-level deep processing skills. The second is the calligraphy of printed characters, seal cutting.
References:
Baidu encyclopedia-seal