Metal alloys are a homogenous mixture of two or more metals, usually combined by melting the metal with the highest melting point and adding the other components in order of their melting points, from highest to lowest. Since the mixture is hotter than the melting point of the added metals, they dissolve into the mixture, forming a new compound with unique properties.

Sterling Silver is a specific alloy containing 925 parts per thousand (.925) pure silver by weight, with 75 parts per thousand (.075) of copper added to make the alloy harder. Items made of this alloy are usually stamped STERLING, .925, or SS. While significantly harder than pure silver, Sterling is still relatively soft, and is sometimes plated with a thin layer of Rhodium to provide a more durable finish. Rhodium is a member of the Platinum family and is significantly harder and more corrosion resistant than silver. Pure silver is also called "Fine silver" or .999 (meaning 99.9% pure) silver.

Karat Gold refers to an alloy containing more than 50% pure gold by weight with the "Karat" value referring to the ratio of pure gold to other metals expressed in 24ths, with pure gold being 24/24ths or 24 karat. 18 karat (18KT) refers to a mixture of 18 parts gold and 6 parts other metals, while 14KT is 14 parts gold and 10 parts other metals and 10KT is 10 parts gold and 14 parts other metals. Expressed as decimals, 18kt is .750 or 75% gold by weight, 14kt is .5833 (58.33%) and 10kt is .4166 (41.66%). As with silver, the primary reason for creating gold alloys is to increase the metal's hardness.

It should be understood that the term karat (KT) used to describe the purity of gold is totally unrelated to the term carat (CT), which refers to a unit of mass commonly used to indicate gemstone weight. One carat, derived from the weight of a carob seed, is equal to 1/5th of one gram. Gem weights under one carat are often expressed in "points", with one point being 1/100th (.01 or "point oh one") carat, so a "25 point" diamond weighs .25 carat (1/4ct).

Electroplating (or just plating) refers to a process that uses electrical current to deposit metal dissolved in a liquid onto metal objects, in essence making the object to be plated act like a magnet to pull metal molecules from the solution. It is important to note that while the plating layer on jewelry items provides an attractive outer layer, it is incredibly thin and does not add any measurable metal value to the item. Plated items are not recommended for items subject to heavy wear, like men's rings.

Gold Filled refers to items that are clad in a layer of gold alloy. Unlike gold plated items, gold filled items are created by pressing a thin outer layer of karat gold over a base metal (usually brass) core. Typically gold filled will be marked with something like "GF 1/20 14KT", which means that the item has a shell of 14 karat gold that comprises 1/20th of the total weight of the item.