The fineness of a precious metal

Precious metal

A precious metal is a rare, naturally occurring metallic chemical element of high economic value.Chemically, the precious metals are less reactive than most elements, have high lustre, are softer or more ductile, and have higher melting points than other metals...

 refers to the ratio

Ratio

In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is...

 of the primary metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

 to any additive

Additive

Additive may refer to:* Additive function, a function that preserves the addition operation* Additive inverse, an arithmetic concept* Additive category, a preadditive category with finite biproducts...

s or impurities

Impurity

Impurities are substances inside a confined amount of liquid, gas, or solid, which differ from the chemical composition of the material or compound.Impurities are either naturally occurring or added during synthesis of a chemical or commercial product...

.

A piece of alloy

Alloy

An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

 metal containing a precious metal may have the weight of its precious component referred to as its fine weight. For example, 1 troy ounce

Troy ounce

The troy ounce is a unit of imperial measure. In the present day it is most commonly used to gauge the weight of precious metals. One troy ounce is nowadays defined as exactly 0.0311034768 kg = 31.1034768 g. There are approximately 32.1507466 troy oz in 1 kg...

 of 18 karat

Carat (purity)

The karat or carat is a unit of purity for gold alloys.- Measure :Karat purity is measured as 24 times the purity by mass:where...

 gold (which is 75% gold) may be said to have a fine weight of 0.75 troy ounces.

Many precious metals are used in the form of alloys. Other metals are added to increase hardness, to make the metal more practical for use in such items as coins

COinS

ContextObjects in Spans, commonly abbreviated COinS, is a method to embed bibliographic metadata in the HTML code of web pages. This allows bibliographic software to publish machine-readable bibliographic items and client reference management software to retrieve bibliographic metadata. The...

 and jewelry, or to decrease the cost of the alloy. For example, copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 is added to the precious metal silver

Silver

Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

 to make a more durable alloy for use in coins, housewares and jewelry.

A traditional measure for the fineness of silver in Britain is the mass

Mass

Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

 of the amount of silver in 12 troy ounce

Troy weight

Troy weight is a system of units of mass customarily used for precious metals, gemstones, and black powder.There are 12 troy ounces per troy pound, rather than the 16 ounces per pound found in the more common avoirdupois system. The troy ounce is 480 grains, compared with the avoirdupois ounce,...

s of the resulting alloy. Britannia silver

Britannia silver

Britannia silver is an alloy of silver containing 95.84% silver, with the balance usually copper.This standard was introduced in England by Act of Parliament in 1697 to replace sterling silver as the obligatory standard for items of "wrought plate"...

 has a fineness of 11 troy ounces, 10 pennyweight

Pennyweight

A pennyweight is a unit of mass that is equal to 24 grains, 1/20 of a troy ounce, 1/240 of a troy pound, approximately 0.054857 avoirdupois ounce and exactly 1.55517384 grams....

s, or about 95.83% silver, whereas sterling silver

Sterling silver

Sterling silver is an alloy of silver containing 92.5% by mass of silver and 7.5% by mass of other metals, usually copper. The sterling silver standard has a minimum millesimal fineness of 925....

 has a fineness of 11 troy ounces, 2 pennyweights, or about 92.5% silver. In other locations fineness is measured in units of mass per thousand. In the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, silver coins often had a fineness of 900, meaning 90% silver and 10% copper.

The fineness (or purity) of gold

Gold

Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

 is commonly measured in carats or karats

Carat (purity)

The karat or carat is a unit of purity for gold alloys.- Measure :Karat purity is measured as 24 times the purity by mass:where...

. The upper end of the scale is 24 carat for 100%. Thus 18 carat = 18/24 = 75%.