Many of the same characteristics that give certain metallic elements high economic value also make them desirable for making jewelry. Compared to common substances such as aluminum and iron, they are rare, making them valuable and expensive. They have an attractive luster, and some resist corrosion, giving them a character that appears eternally beautiful. Although metals comprise many of the elements used to make jewelry, some non-metallic substances are also lustrous, expensive and essential for the jeweler’s art.
Compared to most other elements, gold is extremely rare; according to the University of Georgia, it makes up about 3 parts per billion of the earth’s crust, ranking roughly 73rd out of 92 natural elements in terms of abundance. Unlike iron, copper and other common metals, gold does not corrode in air; in fact, it reacts only with powerful acids such as aqua regia. Its yellowish luster makes gold instantly distinguished from other metals. In pure form, however, gold is too soft to be practical as jewelry; jewelers alloy gold with copper, silver, zinc and other metals to add hardness and other useful properties.
Silver is another precious metal widely used in jewelry. It is also comparatively rare although more abundant than gold. It has a distinctive white luster and can be polished to a mirror-like finish. Like gold, pure silver is relatively soft, bending and breaking easily, so jewelers combine it with small amounts of copper; sterling silver, for example, is 925 parts silver to 75 parts copper, making a durable alloy. Because it is more abundant than gold and platinum, silver is less expensive and accounts for more jewelry, especially lower cost jewelry. Unlike gold, silver combines with air and moisture, forming a thin layer of tarnish, a mild form of corrosion. To keep its lustrous appearance, silver requires periodic polishing with a special chemical cleaning compound that removes tarnish without otherwise affecting the metal.
The rare metal platinum sees use in jewelry as rings, brooches, necklaces and other objects. Harder than gold or silver, it is highly resistant to corrosion. Jewelers mix it with small amounts of similar metals such as iridium or ruthenium to improve its durability. It is denser than gold, making jewelry with significant amounts of platinum heavier than those that use other metals.
Although not a metallic element, carbon in the form of diamond is used by itself and in combination with other materials to make high-quality jewelry. As an element, carbon is one of the most abundant, accounting for 2 percent of the earth’s crust by weight; however, most of it exists in compounds such as carbonates, hydrocarbons and carbon dioxide. Under the extremely high pressures and temperatures encountered inside the earth and from meteorite impacts, carbon forms hard and transparent crystals valued for their durability and beauty as well as their rarity. Unlike the metals, which can be used in jewelry for major structural components, the crystal nature of diamonds make them suitable mainly for ornamentation and embellishing rings, watches and other objects.