You can do what I did! I carefully looked at some dice. First, I noticed that the SIX was always on the opposite side of every die from where the ONE was. And I noticed that every dot on every die was DEPRESSED. That means that a little amount of the MASS of the body of the die had been removed to make the numbers on each die.
This seemed to me that the SIX side of each die must be slightly LIGHTER than the (opposite) ONE side of every die! Since the whole point of shaking and rolling dice is to (allegedly) get perfectly random numbers, we EXPECT to see such randomness.
So me, a really little kid, recruited a neighbor kid to help, and we wrote down how many ones and sixes we saw (hour after hour!) (for the twelve dice we were using, from assorted games) (I did not see any reason to count any other numbers).
A week later, at dinner, I sat on a a BUNCH of sheets of our data! After dinner, I showed all the adults the substantial higher number of sixes (hundreds more!) than ones! (I SHUT UP ALL THE GROWN UPS!)
Yeah, there ARE ways to make dice which are perfectly statically and dynamically balanced. But that is difficult and expensive to do. Hopefully, they do that for the dice used in gambling casinos. But almost every dice you have ever seen or used have probably all been slightly NOT really fair!
Carl W. Johnson, Theoretical Physicist, Physics Degree from University of Chicago