Gold, recognizable by its yellowish cast, is one of the oldest metals used by humans. As far back as the Neolithic period, humans have collected gold from stream beds, and the actual mining of gold can be traced as far back as 3500 B.C., when early Egyptians (the Sumerian culture of Mesopotamia) used mined gold to craft elaborate jewelry, religious artifacts, and utensils such as goblets.
Golds aesthetic properties combined with its physical properties have long made it a valuable metal. Throughout history, gold has often been the cause of both conflict and adventure, the destruction of both the Aztec and Inca civilizations, for instance, and the early American gold rushes to Georgia, California, and Alaska.
About 65 percent of processed gold is used in the arts industry, mainly to make jewelry. Besides jewelry, gold is also used int the electrical, electronic, and ceramics industries. These industrial applications have grown in recent years and now occupy an estimated 25 percent of the gold market. The remaining percentage of mined gold is used to make a type of ruby colored glass called purple of Cassius, which is applied to office building windows to reduce the heat in the summer, and to mirrors used in space and in electroscopy so that they reflect the infrared spectrum.
Golds one drawback for use in industry is that it is a relatively soft metal. To combat this weakness, gold is usually alloyed with another member of the metal family such as silver, copper, platinum, or nickel. Gold alloys are measured by karats. A karat is a unit of equal to 1/24 part of pure gold in an alloy. Thus,24 karat (24k) gold is pure gold, while 18 karat (18K) is 18 parts pure gold to 6 parts other metal, 14 karat (14k)is 14 parts pure gold to 10 parts other metal, and 10 karat (10K) is 10 parts pure gold to 14 parts other metal. The less gold in jewelry the stronger the piece of jewelry is.
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