Noble Metals -Metals that resists corrosion and oxidation.
Malleable - metals that can be worked without powdering or shattering.
Ductile - metals that can be drawn out into thin wire.
To get the appearance of gold without the cost, sometimes jewelry is made with thin coats of gold on less expensive metals. The term "gold overlay" applies to two methods, "gold filled" and "rolled gold plate."
Gold filled pieces have 20% or more gold applied to a base metal. They are described by the amount of gold overlay and its karat. For example, a piece may be stamped 1/20 14K G.F. That means it has a 14 Karat gold layer that makes up one-fifth, 1/20, of the weight.
Rolled gold plate is similar, but the gold can be as thin as 1/40 of the weight. Rolled gold plate is also stamped by its fineness and content, 1/40 14K RGP.
Gold plating is the thinnest and least expensive to achieve the gold look. The gold is a few thousandth of an inch thick at best. These wear off easily.
Platinum Group - includes platinum, iridium, palladium, ruthenium, rhodium, and osmium.
Nickel or German Silver are misnomers, as they have no silver in them at all. Instead, they are various alloys of nickel, zinc and other metals with a silver appearance.
Quicksilver - an ancient term for mercury. "Quick" meaning alive, as in the quick and the dead.
Cupellation - A means of separating gold and silver from other metals and impurities. The ore is heated in a "cupel," (a ceramic cup,) which absorbs the impurities.
Water Concentration - Washing ore causes the heavier metals to stay behind where they can be recovered.
Cementation - To surround a metal with a substance that will react with the metal under heat. Silver is parted from gold by cementation with salt.
Distillation - Metals with a low boiling point, like mercury, are vaporized to separate them from other metals.
Amalgamation - Purifying gold by mixing it with mercury.
Smelting - To melt an ore to separate and refine the metals within it.
Electrum - a natural alloy of gold and silver. It was popular with the ancient Egyptians. Since it is in its natural form and not alloyed, the silver to gold ratio varies.
Niello - a black mixture of silver, copper, lead and sulfur. It is used to fill in designs. It is more like enamel than an alloy.