The mood ring was invented in the 1970s and has a "stone"--actually a chamber filled with liquid--that is said to change colours when the mood changes of the person wearing it. Blue means relaxed, black means stressed and so on. A mood ring stone actually changes colour based on the body temperature of the wearer. Sometimes the colour of the mood ring's stone can get stuck on a certain colour, like brown, which is said to represent a state of restlessness in the person wearing the ring. You can easily fix the ring so it once again changes colour.
Wrap the mood ring in a paper towel and place it in the freezer for two minutes. The paper towel will absorb condensation that may damage the mood ring if it freezes.
Remove the mood ring from the freezer and unwrap the paper towel.
Set the ring near but not directly in sunlight. Let it warm up to room temperature. If the stone is no longer brown, the mood ring is fixed.
This process is not a sure-fire way to fix every damaged mood ring, but it is a common solution for many damaged mood rings. If the mood ring is still brown after you freeze it and bring it back to room temperature, the ring may be irreversibly damaged. If you wish to purchase a new one, the rings are relatively inexpensive.