Troy weight A grain is 20 mites, a mite is 24 droits, a droit is 20 perits, a perit is 24 blanks. In Scotland, the Incorporation of Goldsmiths of the City of Edinburgh used a system in multiples of sixteen. ("See Assay-Master's Accounts, 1681–1702, on loan from the Incorporation to the National Archives of Scotland".) Thus, there were 16 drops to the troy ounce, 16 ounces to the troy pound, and 16 pounds to the troy stone. The Scots had several other ways of measuring precious metals and gems, but this was the common usage for gold and silver. The Pound was
Metallurgical assay on the composition of the rock in which the precious metals are concentrated, and in many laboratories an empirical approach based on long experience is used. A complex reaction takes place, whereby the carbon source reduces the lead oxide to lead, which alloys with the precious metals: at the same time, the fluxes combine with the crushed rock, reducing its melting point and forming a glassy slag. When fusion is complete, the sample is tipped into a mold (usually iron) where the slag floats to the top, and the lead, now alloyed with the precious metals, sinks to the bottom,