Gold has a magic all its own; rare is the person who does not react when hearing that word. Since man’s earliest records, gold has been the ultimate mark of wealth and remains the hallmark jewelry metal.
Pure gold is a very soft and pliable metal. The extreme malleability, ductility, and softness of pure gold make it practically useless for jewelry applications. Jewelry made of pure gold would easily bend and distort in the course of normal wear. To get around this problem, jewelers use an alloyed form known as karat gold (not to be mistaken with metric carat used to measure diamond weight). Alloying increases gold’s hardness and provides a variety of different colors. White gold contains about 10 – 20 % nickel, plus zinc, copper, platinum, and palladium. These alloys make white gold a harder metal than yellow gold. Gold content is specified by the codes 14k, 18k, etc. The K (karat) number specifies how many parts, by weight, of pure gold is contained in 24 parts of the alloy. The purity of gold is most often measured in fineness, but Americans still use the karat. Gold jewelry imported from outside the USA may use fineness instead of karats to describe its purity.
- 10k = 10/24 = 41.67% pure gold
- 14k = 14/24 = 58.33% pure gold
- 18k = 18/24 = 75.00% pure gold
- 24k means 100% pure (or fine) gold
Gold itself is impervious to tarnishing and requires very strong and dangerous chemicals for it to dissolve.
Yellow gold is gold in its natural state, its shades varying with impurities or when alloyed (mixed with other metals), but even white gold is yellow-tinged. White gold can be of several alloys: Nickel is the least expensive, but some people are allergic to nickel. Platinum, iridium and palladium make more expensive, hypo-allergenic alloys. The whitest gold is actually rhodium-plated gold; this plating won’t chip, but does wear off and must be renewed periodically to maintain its best appearance. Other alloys include copper, which makes rose gold and pink gold; silver, which makes green gold; and iron, which makes blue gold. Gold filled is not what it sounds like. It isn’t something filled with gold, it is gold filled with something. Most common is a thin gold sheet heat-bonded to brass; second is gold bonded to silver (this is called vermeil). The gold surface is far thicker than “gold plated”; to be sold as gold filled, gold must be 5 percent or more of the total metal weight. In plating the gold layer is electrostaticly deposited on the base metal and may be just a few microns thin. It can chip and will wear off eventually, but the purchase cost is substantially lower, and replating is more economical than buying new.