You saved up to buy a ring for your special lady, but since you can't afford jewelry store prices, you go through a friend who "has a guy." You meet "the guy" in his small apartment, where he shows you a nice collection of gold, silver and platinum jewelry. The gold rings are stamped 24 karat, so you feel pretty convinced that it's all on the level, believing the story about his uncle's jewelry store and the accidental overstock. In the end, you decide on a nice gold band, which you'll have engraved with some sweet nothings, or something. Your girlfriend loves the ring and all is well, that is until the next day when she wakes up with a green ring finger. Turns out you were taken like a sucker -- the guy your friend knew sold you some fake gold jewelry.
Watching your finger turn green after wearing a gold ring is a surefire way to tell that it's not real. When a customer shops for gold, he or she is informed of its purity by the number of karats, which is what that 14k or 18k stamp on the inside of your ring means. Gold is too soft to hold its shape and withstand day in and day out wear, so it's mixed with other metals to create a sturdier metal alloy. The metals used to make the alloy could be copper, tin, nickel and palladium, just to name a few. The highest rating is 24 karat gold, making it the purest, yet least durable kind.
When you buy a cheap, fake gold ring, it's likely made of mostly copper. When you perspire, the metals in the ring react with the acid in your sweat to form salts, which are green. These acids are essentially causing the copper to corrode on the surface of the metal, which forms a salt compound of the metal. These salts are absorbed into the skin and the result is a decidedly green digit. This is nothing to be worried about; it's not a metal allergy you're suffering from. It simply means that the gold ring you thought was real is really just a cheap imitation. Metal allergies cause redness and swelling, not a dull green color. Another way to spot fake gold is that it can rust in high humidity or over time.