This video shows how you can use what's described as an old golfing trick to check the balance of your dice. You just get a glass of room temperature water, add a bunch of salt until your dice float, and then spin them a few times to make sure you're getting a truly random result.
The DM in me thinks this is a great way to ensure a fair game and to remove any dice that may be rolling low and causing you headaches, but the utter bastard in me is thinking this is a good way to load the odds in your favor.
The whole video is pretty cool, and shows how little care is put into balancing low-cast, opaque dice. Give it a watch, and try to use this knowledge for good and not evil.