Complex sentence: During the Shang and Zhou Dynasties, the material for seal making was mainly animal bones, copper (bronze) and pottery, and there were specially trained, sophisticated artisans or craftsmen, including potters majored in this work-making seals.
Split into simpler sentences: During the Shang and Zhou dynasties the materials for seal making were mainly animal bone, copper (bronze), and pottery. There were specially trained, sophisticated artisans or craftsmen, including potters who specialized in this work, making seals.