Precious metals have been a part of human civilization for thousands of years. Often believed to have mystical powers, precious metal was most attractive as a measure of value (money) and for its beauty. Over time, precious metals came to symbolize wealth, power and strength.

Eight metals are considered precious: gold, silver, and the six members of the platinum family - platinum, palladium, rhodium, ruthenium, iridium and osmium. The National Gold and Silver Marketing Act, first passed in 1906, requires that the manufacturer's hallmark (registered trademark or trade name) be stamped on an item if a quality mark is used.

Following is information about metals used in our jewelry.

Throughout history, gold has been the foundation of many monetary systems and remains important to our economy today. Gold is also a popular metal of jewelry designers because of its versatility. It can be molded, shaped and carved into intricate jewelry designs. Its warm color is very appealing, and it doesn't rust, tarnish or corrode. The major source of the world's gold is South Africa.

Pure gold is so soft that it is rarely used in jewelry, but rather is mixed with another metal - usually copper or silver - to make a stronger gold alloy, or mixture of metals. The amount of pure gold in an alloy is expressed in karats (versus the carat weight used for measuring diamonds and other gems). The higher the percentage of pure gold, the higher the karat. Pure gold is 24K, while 10K gold - the minimum that may legally be called karat gold in the United States - is 10 parts gold to 14 parts other metal. The standard is 14K in the United States, 18K in Europe, and 22K in India, Japan and some other Asian countries.

"Solid gold" refers to an item that contains some gold (at least 10K) and is not hollow. "Gold-filled" is a process by which a layer of gold (at least 10K) is mechanically bonded to a base metal. "Gold-plated" means that an item has a plating (or coating) of gold alloy of at least 10K, though usually less gold than in gold-filled items.

As the karat weight drops, the metal becomes more durable but less yellow. Sometimes gold that is a lower karat weight will be plated in high-karat gold to enhance the color. This is perfectly acceptable as long as you pay a fair price. Keep in mind that gold plating will wear off with time, and the jewelry may need to be re-plated.

The surface of gold jewelry is treated in many ways to enhance the design. Styles like satin, brushed or matte that create soft, lustrous looks to a hammered finish that produces a bright, irregular surface texture offer consumers a variety of looks.

White gold has the same properties as yellow gold, but it has been mixed with different metals to give it a white color. Instead of the copper and silver used in yellow gold, white gold contains metals like nickel, zinc, or even platinum. However, white gold should not be confused with platinum, which is much rarer than gold and hence more valuable.

The same karat weight system is used for both white gold and yellow gold. While 18K yellow gold and 18K white gold contain the same proportion of gold; only the remaining 25 percent of the alloy is different. Sometimes white gold is plated with an even whiter metal, such as rhodium (a very rare member of the platinum family), to enhance its appearance.

White gold was developed to give a different look to jewelry. The white color is an excellent setting for very white diamonds, and when used side by side with yellow gold, it creates a striking effect. Jewelry using both white and yellow gold is called "two-tone."

The most precious metal used in jewelry is platinum. Heavier, more rare and more durable than gold, platinum is very expensive and is alloyed with other precious metals for added strength. Platinum jewelry is usually produced from an alloy of 90 percent platinum and 10 percent iridium, two of the precious metals in the platinum family. The other members include palladium, ruthenium, osmium and rhodium (also used for plating because of its extreme whiteness).

Because of its purity, platinum is excellent for people who are allergic to other metals. Platinum will never tarnish or wear out, and its light color makes it popular for jewelry. Like white gold, platinum settings make white diamonds appear very bright; however, platinum is whiter in color and heavier than white gold.

Used extensively in jewelry throughout the first half of the 20th century, platinum was banned for use in non-military applications during World War II. However, it has enjoyed an enormous resurgence in popularity in recent years. Mined in Africa, Russia and the United States (Montana), platinum is not sold according to karat weight. Platinum jewelry that is stamped with a quality mark also shows the percentage of platinum used in the alloy - for example, Pt1000, 1000Pt or 1000Plat for pure platinum; or Pt950, 950Pt or 950Plat for 950 parts per thousand platinum and 50 parts other metals.

The standard for sterling silver has remained unchanged since 1300 when Edward I of England established an early trade practice rule for silversmiths, decreeing that sterling must consist of 92.5 percent pure silver alloyed with 7.6 percent copper. The term "sterling" refers to the composition of the metal, never to the weight of a finished item.

Silver is much more plentiful than gold; however, silver tends to tarnish, making it less popular in some forms of jewelry. Like gold, silver is too soft for use in its pure state and must be combined with other metals for durability. Jewelry made of silver parts and gold parts must carry dual designations such as "Sterling and 10K."

As a general rule, most jewelry is easily maintained by wiping with a soft, clean cloth to retain its luster and beauty. Avoid contact with perfume, soap, hairsprays and cosmetics.

Most silver jewelry can be cleaned with a simple solution of two parts ammonia and one part water (preferably distilled). Use a soft cloth to rub away tarnish after the piece has soaked for about one minute.

Chlorine can damage gold so avoid wearing gold jewelry in swimming pools or hot tubs, or while using chlorinated cleansing products like bleach. Remember to store metal chains flat to prevent kinking or breakage.

Rubbing alcohol can be used to clean mountings, though soap and water used with a soft brush will take care of most of your jewelry cleaning needs. Be sure that the brush is very soft when used on metal - especially gold, which can be easily scratched. Then dry and buff your jewelry with a soft cloth that won't leave behind any fuzz or threads.

NOTE: Do not use any type of chemical or alcohol cleaner with jewelry that contains pearls (real or cultured) or opals. (Refer to the Colored Gemstone section for further information about gem care.)

These are machines that clean jewelry by bombarding it with sound waves. This vibration shakes off dirt, but the vibrations can also cause damage to the jewelry. The inclusions in gemstones, especially brittle stones like emeralds, can be greatly enlarged by the shaking, making the stones less attractive and less valuable. Soft gems like pearls should never be put in an ultrasonic cleaner. Because of the risk, we recommend caution when using ultrasonic cleaners.