For most of history, the value of a coin depended on its intrinsic value — on the weight and purity of the metal from which it is made. Various methods were used to maintain, safeguard and verify that value:
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the reputation of the authority (or government) issuing the coin |
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security measures to prevent forgery — in particular, milling around the edge to prevent the inside being filled with base metal or plaster |
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the practice of assaying, to test the quality and purity of the metal in the coin — whether by government authorities or by financial professionals. |
In nineteenth-century Hong Kong, and in other Chinese ports, assaying was carried out mainly in the private sector by shroffs employed by banks and other businesses or acting as independent money-changers.
With the gradual decline of gold and silver coinage in the early twentieth century — and the decline in the real value of coins — maintaining the integrity of a coin has become largely a matter of security features in the design (particularly in the milling and edging) and of the choice of alloy used in manufacture.
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