Gold
Gold in its pure state is seldom used for jewelry as it is too soft. It is combined with other metals (alloys) to produce a more durable metal. The presence of other metals in gold produces the various colors of gold. Copper, for example, adds a reddish tint. Nickel and copper with zinc turn gold white.
Karatage
Pure gold is stated as 24 karat. Each karat represents 1/24 of pure gold.
The gold content of an 18K jewelry item is therefore 18/24 or 75% pure gold.
According to the European system, 18K gold is marked 750, 14K gold is marked
585, 10K gold is marked 420.
10K gold is the lowest percentage allowed to be marked and sold as Karat
Gold Jewelry in the United States. Underkarating (stamping a karatage as
higher than the item actually contains) does occur, but most of it goes undetected
because it is not possible to analyze gold jewelry for its karatage without
damaging the jewelry in the process.
Platinum
Platinum is one of the softest metals. But when it is alloyed with other metals, normally 10% iridium, it becomes one of the hardest metals. This hardness makes platinum ideal for jewelry with diamonds and other valuable stones because it provides the most secure material for setting gems.
Left to right: Silver, platinum, 18k white gold
Platinum is white in color and is often mistaken for white gold. However,
platinum carries higher costs than gold because it is denser and is more
difficult to fabricate, due to its higher melting point.
(U.S. law governing trademarks and
quality marks for gold and silver do not yet apply to platinum, but this
is being changed. Europe and Canada already include platinum in their marking
laws.)
Silver
Silver is the whitest of the precious metals and the most lustrous. It reflects 95 percent of the light that hits it, compared with 92 percent for gold. Next to gold, silver is the most malleable metal — it can be formed into sheets (or leaves) .00025 millimeter thick. It is second only to gold as a ductile metal — a gram of silver can be drawn out into a wire a mile long.
Silver in its pure form is almost never used in jewelry because it is too soft. It also has a tendency to tarnish.
The addition of a very small amount of copper increases the durability of silver. British silversmiths discovered that an alloy of 925 parts silver and 75 parts copper was ideal, hence the term "sterling standard." Items stamped "sterling" meet this purity standard, as set forth in the National Gold and Silver Marking Act. Sterling silver is also called silver, sterling, or solid silver.
