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Sterling silver is an alloy of silver containing 92.5% by weight of silver and 7.5% by weight of other metals, usually copper. The sterling silver standard has a minimum millesimal fineness of 925.
SILVER, for example 99.9% pure silver, is relatively soft, so silver is usually alloyed with copper to increase its hardness and strength. Sterling silver is prone to tarnishing, and elements other than copper can be used in alloys to reduce tarnishing, as well as casting porosity and fire scale. Such elements include germanium, zinc, platinum, silicon, and boron. Recent examples of alloys using these metals include argentium, sterlium, sterilite and silvadium.
Red coral (Corallium Rubrum) comes from certain areas, such as the Mediterranean, where the specific water temperature and conditions allow coral to thrive. Coral is a hardened tube or branch. Only about 10% of coral is considered jewelry quality. Coral comes in shades from blood-red to orange to pink to white.
Although coral has been used by Stone Age peoples as long as 30,000 years ago to decorate sepulchers (burial vaults), Native American artists have only used coral for the last 600 years.
Morenci turquoise is another American classic, highly regarded and sought after by collectors. Though the Morenci turquoise mine produces a wide range of colors from blue to green, the most desirable is a deep blue color with a heavy iron pyrite matrix and occasionally some spider webbing.
The Morenci turquoise mine is located in Southeastern Arizona. It is the by-product of a large open-pit copper mining operation and dates back to 1864. William “Lucky” Brown was offered the mining rights in the 1950s and the Brown family has worked the mine since. Though no turquoise is actively being produced at the Morenci mine, small amounts do still come to market each year from the stock that was mined previously.