Short answer: the development process of the calligraphy style of bronze inscriptions.

The common inscriptions on bronzes of three generations, also known as Zhong Dingwen, belong to one of the great seal scripts. There were few inscriptions in the Yin and Shang Dynasties, mostly ancestral names or clan totem symbols, and their styles were closer to Oracle Bone Inscriptions. From the late Shang Dynasty to the Western Zhou Dynasty, a large number of monumental inscriptions appeared, with complete font structure, concise strokes, strong lines, rich, round and neat. Since the Eastern Zhou Dynasty, hieroglyphics have become longer and more decorative. During the Qin and Han dynasties, the inscriptions on bronzes were mostly imperial edicts, with regular characters and thick lines, representing official fonts, with royal flavor and artistic decoration. After the Western Han Dynasty, bronze inscriptions gradually declined and became unsystematic.