If a list was made of favorable characteristics for a suitable jewelry metal it would certainly include requirements for beauty as well as high resistance to wear and chemical attack. Such a metal would have to be workable into complex forms. It should be generally available, but not so common as to be uninteresting. Surprisingly few metals meet all these qualifications to any degree. Gold diamond jewelery places first; silver and platinum just about complete the list. These three metals and their alloys—mixtures with baser metals—are exclusively the metals of quality jewelry. Relatively minor amounts of the bright and durable metals palladium, ruthenium, and rhodium are also pressed into service with the noble metals. An indication of the difference in attitude toward these noble metals is the fact that they are customarily not even weighed by the same system. Gold, platinum, and silver are measured by troy weight, while copper and others are scaled with standard avoirdupois weights. A troy ounce is about 10 percent heavier than an avoirdupois ounce and there are only twelve ounces in a troy pound. For everyday use we are much more accustomed to the sixteen lighter ounces in an avoirdupois pound.