I often get asked about different metals, what they are, and how to care for them so I decided to compile a few of the things that I have learned over the years. Most metal will oxidize. There are several ways to do this.
Copper- Copper has a reddish gold look to it and is rarely labeled. It is one of the oldest used metals because it is present in nature without having to extract it from an ore. Because it is present in most living animals it has gained a reputation for its medicinal uses. When copper is exposed to air there is a chemical reaction that happens where it actually looses some of its hydrogen. This chemical reaction turns it green and is called a patina. This patina can actually protect the copper from breaking down. Or if you are wearing a pieces of copper this patina can stain your skin. The Statue of Liberty is a great example of the green patina on copper. Copper is also a great conductor of electricity and is found is building materials and wires. This fact combined with the vast amounts of copper naturally found at the Grand Canyon leads it to being one of the places most struck by lightning. The best way to care for copper jewelry is to wear it, allowing your skin and daily activities to be its polish cloth. You can seal the copper from being exposed to the elements. One of the easiest ways of doing this with jewelry is to paint it with a little clear nail polish.
Brass- Brass is an alloy of Copper and Zinc creating a dark gold color. This gold color makes it a great economical replacement for gold in jewelry. It will either be labeled as brass or not labeled at all. Brass, like copper will oxidized easily (because of its copper content) , and turn black. Brass will also turn some people green for the same reasons stated above. Again, you can put a clear coat of lacquer or some nail polish on your jewelry to protect your skin.
Sterling Silver- Sterling silver is an alloy of 92.5% silver and usually copper. In the United States a metal can not be labeled as sterling if it contains any nickle. (There is another metal called nickle silver- I don't use) Sterling silver will have the stamp of .925 on it*. There is FINE Silver that is 99.9% silver but can be a bit soft for everyday jewelry use. Because sterling is mixed with copper it will oxidize as explained above.
Gold- Gold is a natural occurring element that is a bright, rich, yellow. The origin of the gold will affect the color but most people will not notice. Gold is measured in karat weight in 24 increments. 24 Karat gold is pure gold. The karat of gold will be marked 10k, 14k, 18k, 22k, and 24k. Copper is usually the alloy that is mix with the gold to make it harder. Because of this the lower karats will oxidize.
Plating- Plating is done in either silver or gold. The gold and silver are adhered by electricity or sprayed on to a base metal of copper or brass. The thickness is between one and 2.5 microns of an inch. Over time the plating will rub or flake off.
Gold Fill- Gold filled or "Rolled Gold" is a process in which a base metal is rolled in gold so the outside 20% is gold. This thickness is significantly thicker than plating and can last years before it starts to rub through. This will be marked with the gold karat above the 20% for example 14/20 is for 14kt gold fill.