In 1886, a young stamp collector in Sweden was looking through old letters in his grandmother’s attic when he made a promising discovery. It was a 3 skilling (equivalent to 3 cents) stamp from the country’s first run of postal stamps thirty years earlier. He quickly sold it to a collector, who was puzzled by the stamp’s yellow color: the 3 skilling denomination was supposed to have been printed in blue-green ink, with yellow being used for the 8 skilling version. Over the years, it became clear that the misprinted yellow stamp was the only surviving one of its kind, and its price skyrocketed accordingly. In 2010 it was purchased by an anonymous buyer for “at least” $2.3 million. That means the going rate for that little slip of paper is approximately $2.55 billion per ounce! Compare that with an ounce of gold, which on the same date was selling for a mere $1,180.