Recently, a man wanted to sell some old gold filled jewelry that he had inherited from an elderly aunt. There were actually quite a few items - a bracelet, a few old rings, a necklace with a pendant attached, a small decorative pin, and a few other items. So the man put all those items in a Manila envelope, got in his car, and drove to a store that displayed the sign, “We Buy Gold.”

We’ve already written about pink gold, rose gold, white gold, and even green gold on the Specialty Metals blog. (See related posts below.) We thought we’d seen just about every color, then we found an article entitled “What Can Make a Piece of Gold Turn Blue?” that Esther Inglis-Arkell wrote for io9.com.