Copper seals were most prevalent, while the iron seals used by high officials proved less suitable as they were subject to rust and oxidation. The so-called 'gold' and 'silver' seals were actually plated copper seals.
漢代對各級官吏所用印章的材質均有規定，如相國、丞相等都用金印，御史大夫及官秩在二千石以上的則用銀印。