Precious metal "precious" metal can also be determined by high demand or market value. Precious metals in bulk form are known as bullion and are traded on commodity markets. Bullion metals may be cast into ingots or minted into coins. The defining attribute of bullion is that it is valued by its mass and purity rather than by a face value as money. 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
The Aurum Film Encyclopedia through 1990 and a different set of appendices. Ten pages were added to the new edition, covering the few films produced during the years 1984 - 1990. This edition was reprinted in 1995. Published in 1984, "The Aurum Film Encyclopedia: Science Fiction", followed the history of the genre chronologically, from 1897 – 1983. Unlike the previous volume, silent genre titles are included, and even minor genre films are reviewed in the main text. Also unlike the first volume, Hardy mentions the names of the various critics who provided the reviews in the text, which in this book were Denis Gifford,