Precious metals The exact purity of very fine precious metals such as
platinum,
gold and
silver can be of great interest. Based on the system of
millesimal fineness, a metal is said to be
one nine or
one nine fine if it is 900 fine, or 90% pure. A metal that is 990 fine is then described as
two nines fine and one that is 999 fine is described as
three nines fine. Thus, nines are a
logarithmic scale of purity for very fine precious metals. Similarly, percentages ending in a 5 have conventional names, traditionally the number of nines, then "five", so 999.5 fine (99.95% pure) is "three nines five", abbreviated 3N5. Canada's
Big Maple Leaf, a coin made of gold at 5N (99.999%) purity, stands as the purest gold coin ever minted, anywhere. The purest gold ever achieved was reportedly produced at the
Perth Mint in 1957, at "almost six nines" (99.9999%) purity, as measured by the
Worshipful Company of Goldsmiths of London.
Gases The nines scale is also used in other contexts, such as describing the purity of
gases. The purity of a gas is an indication of the ratio of it to other gases in its
mixture, as measured by volume. Thus, a high purity refers to a low amount of other gases, or impurities. Gases of higher purity are in many contexts considered to be of better quality and are usually more expensive. The purity of a gas is generally expressed as a grade prefixed with the letter N (rather than postfixed), indicating the "number of nines" in the
percentage or
decimal fraction. For example, a N2.0 gas is 99% (two nines) pure and 1% impurities by volume; a N6.0 gas is 99.9999% (six nines) pure, with 1
part per million (1 ppm or 1 vpm, volume per million) impurities. Intermediate values indicate the digit following the last nine. For example, N4.6 estimates a purity level of 99.996% (four nines followed by a six). A "five nines" (99.999%) uptime describes a system that is unavailable for at most 26 seconds per month. ==References==