of the 40% silver coins began to exceed their face value, which resulted in a repeat of the previous event, as the 40% silver coins also began to vanish from circulation and into coin hoards. A similar situation occurred in 2007, in the United States with the rising price of copper, zinc, and nickel, which led the U.S. government to ban the melting or mass exportation of one-cent and five-cent coins. In addition to being melted down for its bullion value, money that is considered to be "good" tends to leave an economy through international trade. International traders are not bound by legal tender laws as citizens of the issuing country are, so they will offer higher value for good coins than bad ones. The good coins may leave their country of origin to become part of international trade, escaping that country's legal tender laws and leaving the "bad" money behind. This occurred in Britain during the period of adoption of the gold standard - in 1717 Isaac Newton, then Master of the Mint, declared the gold guinea to be worth 21 silver shillings. This overvalued the gold guinea in Britain, making it "bad", and encouraged people to send "good" silver shillings abroad, where it could buy more gold than at home. This gold was then minted as currency, which bought silver shillings, which were sent abroad for gold, and so on. For a century hardly any silver coins were minted in Britain, and Britain moved onto a de facto gold standard. History of the concept Gresham was not the first to state the law which took his name. The phenomenon had been noted by Aristophanes in his play The Frogs, which dates from around the end of the 5th century BC. The referenced passage from The Frogs is as follows (usually dated at 405 BC): According to Ben Tamari, the currency devaluation phenomenon was already recognized in ancient sources. He brings some examples which include the Machpela Cave transaction and the building of the Temple from the Bible and the Mishna in tractate Bava Metzia (Bava Metzia 4:1) from the Talmud. In China, Yuan dynasty economic authors Yeh Shih and Yuan Hsieh (c. 1223) were aware of the same phenomenon. Ibn Taimiyyah (1263–1328) described the phenomenon as follows: Notably this passage mentions only the flight of good money abroad and says nothing of its disappearance due to hoarding or