KNOW THYSELF. And if you can't tell what the hell you're feeling, let these vintage earrings be your guide. Mood rings (and earrings, apparently), were based on a liquid-crystal technology invented in 1975. The theory was that your body heat fluctuates with your state of mind, which then changes the color of the stone. A printed guide was always included to help you decipher the code: for example, blue-green means "emotionally charged, and somewhat relaxed". No wonder that mood jewelry was such a huge (but short-lived) fad. We were thrilled when we found a huge cache of forgotten liquid-crystal stones mounted in gold-plated earring bases. You'll get your pair with their original guide, "Interpreting the Color Code". They measure just over 1/2" wide, and they still "work" perfectly!