The majority of these bronze coins are of the type known as spade currency. This is because they resemble spade tools and were in fact cast in similar moulds to the tools themselves, although the coins are smaller and thinner and the metal used is of a different composition. The first spade coins originated in the 6th or 7th century BC in the Zhou Middle Kingdom, and the concept spread throughout much of China in the next 300 years. The coin at top right is a knife coin, again so called because of its resemblance to the tool. As with the spade money, different states produced hundreds of different forms of these coins. It is thought that these styles of coin evolved from an earlier practice whereby the actual tools themselves were used as a medium of exchange.
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