Gold is one of the most precious metals in
the world. It is present in the rivers, seas, and the earthís crust
and trace amounts are present in plants and animals. It is, however,
difficult and expensive to extract. In modern mining operations
approximately 3 tons of ore are needed to extract one ounce of gold.
The many desirable qualities found in gold, along with its scarcity,
have made it the most popular metal for use in jewelry today.
Properties of Gold
Gold in its pure state:
Has a melting point of 1945 degrees
Farenheit (1063 degrees Celsius). When alloyed (chemically
combined) with other base metals the melting temperature of the
resulting alloy is changed. 18K yellow gold has a melting point of
1675 degrees Farenheit and 14K yellow gold has a melting point of
about 1550 degrees Farenheit.
Has a specific gravity of 19.33. It
is relatively heavy compared to most metals, such as silver (SG
10.7) or iron (SG 7.8). A notable exception is platinum (SG 21.4).
Is more malleable than any other
metal and can be hammered into foil so thin that it is almost
Has a unique ductility property
allowing it to be drawn into wire so fine it can barely be seen.
Is deep yellow in color. Its great
reflectivity properties help keep its brightness and color from
fading with time.
Will not rust, tarnish or corrode.
Gold jewelry recovered from ancient Egyptian tombs is in the same
state as when placed there over 4000 years ago.
Is softer than most other metals. On
the Mohs scale of hardness (which is a measure of a gemstone or
mineralís resistance to scratching), gold has a hardness value of
2 to 2.5. Diamond has a value of 10. Pure gold may easily be
scratched. Fortunately, gold becomes harder when alloyed with
other base metals.
Is relatively scarce and therefore
expensive. It is estimated that only 125,000 tons of gold have
been mined the world over since the beginning of time.
Is able to bond with other base
metals. This property gives rise to the many different colors
available in modern gold alloys.
Fineness (Karat Value)
Since ancient times the purity of gold has been
defined by the term karat, which is 1/24 part of pure gold by
weight. Pure gold is equivalent to 24K. Gold purity may also be
described by its fineness, which is the amount of pure gold in parts
per 1000. For example, a gold ring containing 583 fine gold has 583
parts (58.3%) gold and 417 parts (41.7%) of other base
Federal Trade Commission rules require that all
jewelry items sold in the United States as gold shall be described
by "a correct designation of the karat fineness of the alloy." No
jewelry item less than 10K may be sold in the United States as gold
The following table lists the relationship between
different international gold markings.
Fineness of Gold Karats
Weighing Precious Metals
The weight of a piece of gold jewelry is a factor
that helps to determine its value. It is important because it is an
indication of the amount of fine gold in an item of jewelry. Grams
(g) and pennyweights (dwt) are the units of weight most commonly
used in weighing gold. Gold and silver are almost always weighted in
the troy system of weights where one pound troy equals twelve troy
ounces and twenty pennyweights equals one troy ounce. The
Avoirdupois weight system, where one pound equals 16 ounces, is used
in the United States for most everything except precious metals. The
following table summarizes useful weight conversions.