Precious Metals - A Brief Lesson In Metallurgy
Gold is an element found in nature in metallic form with a rich yellow color. The purity of gold is measured by its karat (not to be confused with "carat", which refers to the weight of a gemstone). In nature, gold mined from the earth is rated as 24 karat, the highest purity available. When used in jewelry, the 24 karat gold is mixed with different metals to form an alloy to which makes it more suitable for everyday wear. Most jewelry that is made from gold is either 14 karat or 18 karat. While 18 karat is more pure and more yellow in color, it is also a softer material than 14 karat. Even though they exhibit slight differences, both 14 karat and 18 karat gold are beautiful and well suited for jewelry due to the ability to polish to a high luster. Different alloy colors include White, Pink (Rose), and Green. All colors are available in 14 karat and 18 karat.
Platinum is another element found in nature in metallic form. It has a naturally white color, and is very dense. When used in jewelry, platinum is usually 90 - 95% pure. It is usually alloyed with either Iridium or Ruthenium, which are two other "Platinum Family" metals. It is very rare, and desired for jewelry due to it's naturally beautiful white color and it's distinctive feel of heaviness due to it's density when worn. Also, because of the degree of purity used in platinum jewelry, it has a very low incidence of causing an allergic reaction.
Silver is also an element found in nature in metallic form. The least rare of the 4 precious metals, silver jewelry is relatively inexpensive when compared to Gold or Platinum. When used in jewelry, silver is usually alloyed into Sterling Silver, which is 92.5% pure. It exhibits a highly lustrous, naturally white color which makes it quite desirable and well suited to the jewelry industry. It is very soft, and is easily bendable. One common issue with silver is it's tendency to tarnish or oxidize, which is caused by a reaction of the metal with air. Although it tarnishes, it is easily polished and can be restored to it's original luster.
Rhodium is another "Platinum Family" metal that is used widely throughout the jewelry industry. It's most common usage in jewelry is to provide a bright white color and high luster plating to white gold jewelry. It is applied through electrolysis, and bonds well to its gold host. Eventually, this plating will being to wear away, but not to worry, as it can be restored to it's original condition by polishing and re-applying the rhodium.