Makes me wonder the extent to which the rolling surface would affect the outcome. A harder surface would cause more bouncing. Would more bouncing increase or decrease the relative fairness?
One common test of a die's fairness is floating it in salt-water, which allows any irregularity in the weight distribution to show itself. From that, intuitively I would assume that zero resistance (as much bouncing as possible/needed) would result in the unfairness making itself most apparent. Meanwhile, zero bouncing would cause the die to stick where it lands, making any unfairness the result of how it was thrown, and it's easier to cause a lot of randomness in that regard.
That said, I'm not sure that's generalizable to more realistic amounts of bouncing ("only a bit of bouncing" as opposed to "none at all", and "kinda a lot of bouncing" as opposed to "effectively zero resistance").
I've never actually heard of the salt water test. It makes sense thinking about it. I got a bag of dice from my dad, from his d&d days, from when he was younger than me. There's a huge mix of some really weird dice in there. They're fairly worn, some of the numbers aren't visible any more, and their original quality ranges wildly. I wouldn't mind dropping them all in a bucket of salt water to see now. I've drawn my own conclusions about them over the years of using them, it'd be interesting to see how well they match up.
Also, i wonder how my dad's homemade d20, made out of a double d10(d20 with 0-9 twice, 0's used as 10 and 20) with half the numbers coloured red(11-20 is red), with a pen, would rank up, it was likely just done randomly.
If you're going to do the salt water test, only use a glass of water, not a bucket. It takes quite a bit of salt to make the density of the salt water higher than most dice.
As far as I know continued bouncing would give the d20 more time to find its center, so it would be less random. That's pretty much the whole idea behind Gamescience dice. They aren't tumbled, so the edges are sharp and sometimes there's exposed mold flashing, but they stop rolling faster, meaning they're less likely to find their center
I don't know, but I used to play boardgames with a guy who would always try to do that. He'd hold the dice in his fingers so they couldn't move and would shake his hand, but the dice wouldn't change position. Then he'd just kind of drop them so they might not roll. He was successful sometimes in that it would give him a good outcome, but also there were like 4 other people around the table watching this, so we'd make him roll for real if the dice didn't move.
