Nine-jo seal script

...Private seals and official seals took two opposing directions. In order to prioritize practicality and make private seals easier to read, characters were used not only in seal script, but also in clerical script, regular script, and even cursive script. On the other hand, official seals became clearer after the Song dynasty, but their size changed from a square 3cm square to 2-3cm square to give the seal impression authority and prevent counterfeiting, and the characters became a dense style of writing called nine-tatami seal script, in which the strokes are curved and folded. During the Song dynasty, epigraphy developed greatly, and research on ancient seals began along with the ancient bronze artifacts that began to be excavated in large numbers around that time....

*Some of the terminology used in reference to "Kujoten" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…そしてそれは私印と官印とで相反する二方向をとり，私印は実用を優先して判読しやすくするため，文字は篆書ばかりでなく，隷書，楷書，さらに行書，草書まで使用されるようになった。一方，官印は宋以後になるとより鮮明になるが，印影に権威を帯びさせ，偽造を防ぐために大きさは方寸(3cm四方)から方2～3寸に変わり，文字は筆画が屈曲折畳する九畳篆と呼ばれる繁密な書体になった。　宋代には金石学が非常に発達し，そのころさかんに出土しだした古銅器とともに古印の研究が始まった。…

※「九畳篆」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報