Editing Precious metal (section)

===Purity and mass===
[[File:Johnson Matthey 500 grammes silver bullion.jpg|thumb|left|500&nbsp;g silver bullion bar produced by [[Johnson Matthey]]]]

The level of purity varies from issue to issue. "Three nines" (99.9%) purity is common. The purest mass-produced bullion coins are in the [[Canadian Gold Maple Leaf]] series, which go up to 99.999% purity. A 100% pure bullion is nearly impossible: as the percentage of impurities diminishes, it becomes progressively more difficult to purify the metal further. Historically, coins had a certain amount of weight of [[alloy]], with the purity a local standard. The [[Krugerrand]] is the first modern example of measuring in "pure gold": it should contain at least {{frac|12|11}} [[Troy ounce|ounces]] of at least {{frac|11|12}} pure gold. Other bullion coins (for example the [[Sovereign (British coin)|British Sovereign]]) show neither the purity nor the fine-gold weight on the coin but are recognized and consistent in their composition.{{Citation needed|date=January 2010}} Many coins historically showed a [[denomination (currency)|denomination]] in currency (example: American [[double eagle]]: $20).