This is an article I wrote for JewelryLessons.com
Gold is a popular metal for jewelry making, but there are many different colors, alloys,etc, which can sometimes be confusing for people when they trying to decide which to use for their work, so I have written this article to shed some light on this beautiful metal.
Gold has been used for ornamentation since prehistoric times throughout the world. Ancient Egyptians described it in hieroglyphics more than 2000 years BC, it is frequently mentioned in the Old Testament, and was used for coins in China as early as the 5th or 6th centuries BC. Early, primitive methods for mining gold included fire-setting; where fires were set against the rocks, then quickly doused with water, causing the stones to crack open, and making it easier to extract from the surrounding rock. The Romans developed large scale extraction techniques using large volumes of water to dislodge rocks and sediment. The exploration of the Americas was fueled by reports of golden ornaments worn by the peoples of Central America, Ecuador, Peru and Colombia.
Gold is dense, soft, shiny, and extremely malleable and ductile, meaning it can be deformed plastically without fracturing. One single gram of gold can be beaten into a sheet one square meter in size, and it can be beaten thin enough to become translucent. These qualities make it highly suitable for jewelry making. Pure gold has a beautiful, bright yellow color. In fact, gold, copper and caesium are the only metals that have a natural color other than gray. Because if its atomic structure, it resists corrosion, and it also readily creates alloys with other metals. The chemical symbol for gold is Au, from its Latin name aurum.
Pure gold is generally too soft to be used for jewelry, so other metals are almost always added to it, and the colored alloys are just as 'real' as yellow gold. Different metals can give the gold different colors. For instance, gold alloyed with mostly copper will give the gold a pink or rose color. Gold alloyed with iron will give a blueish colored gold (though this alloy isn't used much, as it tends to be brittle, and difficult to work). When alloyed with nickel or palladium, it takes on a white color, and green gold is made by alloying it with silver. 24K gold is pure gold. 18K gold is 75% gold and 25% other metals, 14K gold contains 14 parts gold and 10 parts other metal(s), making it 58.3% gold. 12K gold is made from equal parts gold and other metals, making it 50% gold. 10K gold is the minimum karat designation that can be still called gold in the United States, and has 10 parts gold and 14 parts other metals, making it 41.7% gold
Rolled gold, or gold filled, is a laminate of gold sheet (usually between 12K and 18K) which is fused to a base layer (usually brass). The quantity of gold used is sometimes indicated by a fraction, such as 18K 1/5, which would indicate a laminate that is 1/5 18K gold by weight. With gold filled, the gold layer is much thicker than the microscopically thin layer laid down by electroplating, and is, thus, more resistant to wear. Often the layer of gold on gold filled is thick enough that it can be engraved without exposing the base layer. Vermeil, which is sometimes called silver gilt, is sterling silver covered with a coating of gold. The gold content must be at least 10K, and at least 1.5 microns (millionths of a meter) thick for an item to be called vermeil. It is usually produced by fire heating or electrolysis, the latter being the most common today, as fire heating can emit mercury vapors, which are harmful.
Whether you choose to use solid gold or gold filled for your work, know that you are joining countless artisans throughout history in incorporating this beautiful metal in your work. Enjoy!