Complex sentence: From the 6th century AD and later new "mother coins" ("mǔ qián") were cast for future coins to be based on, these were engraved in generally easily manipulated metals such as tin.
Split into simpler sentences: From the 6th century AD and later, new "mother coins" ("mǔ qián") were cast as the basis for coin production. These were engraved in generally easily manipulated metals such as tin.