What does the iron painting silver hook mean?

Describe the vigorous and feminine calligraphy. The word "iron-painted silver hook" first appeared in the calligraphy works of Liu Gongquan, a scholar in Tang Dynasty. It describes the artistic conception of calligraphy with images such as scenery and objects, organically combines calligraphy with natural objects, endows calligraphy works with agility and charm, makes calligraphy art more vivid, vivid, vigorous and feminine, and becomes an artistic form with artistic conception.