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Do crystal shaped dice (example) provide any notable advantage or disadvantage over traditional hobby dice shapes (example)? Are they equally random?

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You can't stab your foot on a d4... –  Random832 Nov 29 '11 at 19:10
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If you have e.g. 10 d10 crystal dice and otherwise traditional dice, it is easier to find those d10 (or what kind soever) in that huge heap of dice. (You're role-playing, you got a heap of dice, right?) –  Stephen Nov 29 '11 at 19:43
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In the early runs, the crystal d20s had a design flaw that ensured that one of the numbers could not be rolled — the face was opposite an edge, and the die would roll to one of the numbers beside it. –  Jadasc Nov 29 '11 at 19:52
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@Random832, as a rogue, I say that those d4s come in handy when you forget your caltrops... –  fire.eagle Nov 29 '11 at 22:16
    
How far do hey roll? I noticed that the crystal d6 I got in Dragon magazine comes to a stop much more quickly then traditional ones. –  Canageek Nov 30 '11 at 0:55

4 Answers 4

up vote 15 down vote accepted

Short answer: there's no real difference between the two types.

The type of dice you're calling crystal are also known as rolling-pin or rolling-log style dice. They're actually just n-sided prisms with the ends tapered so they never land on them. Rolling a prism die like this is just as fair as any other die.

To see why, take a look at a picture of a prism -- Wikipedia's article on pentagonal prisms, for example.

In that article, there's an image of a 5-sided prism at the upper right. A die in this shape would have 5 rectangular sides around it, and 2 pentagonal ends. If the ends are convex enough (like the "crystal" dice of your example link), then the die can never land on them. This leaves only the 5 rectangular sides as options. All of them are evenly distributed around the "waist" of the die, and all of equal size. Therefore, they're all just as likely of landing points.

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Totally this. No statistical difference, but you get plenty of style points if you roll with the rolling pin dice (or other unusual dice). –  Pulsehead Nov 29 '11 at 18:49

Two things:

  • If dice are symmetrical and of uniform density, it doesn't matter which material are they made of. The problem with cheap dice is that they're usually not manufactured up to exacting standards.
  • [snark]If the rolling-pin dice they sell have the quality of their website design...[/snark]

Do note that the density and symmetry problem can show up on both kinds of dice. Just because they can't land on some ends doesn't mean they're good dice.

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I think it is definitely worth testing your dice for 'honesty' if you doubt them, but do this when you're bored, not during your weekly rpg-sessions. You'll need to go dig up some statistics lessons on hypothesis tests anyway so... –  Jo Heymans Nov 29 '11 at 21:12
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@okeefe, that d12 promised me there was a +10 sword of gleaming awesomeness in that cave last adventure. Three ghoul bites and a broken arm later, and I'm beginning to mistrust my dice. –  Joe Nov 30 '11 at 2:06

There are several key advantages to barrel shaped dice:

  1. Not limited to even numbers
  2. only roll in one linear direction
  3. are slightly easier to spot untrue dice amongst (roll it down a 30-40° drum, and uneven ones will not make a steady sound! Discovered by accident at work.)

Disadvantages:

  1. tend to be larger for a given number of sides
  2. hard to tell number of sides at a glance (esp d10 vs d12)
  3. larger (d20 & up) ones can be hard to determine the "up" face on
  4. more expensive (both due to more material and fewer produced)
  5. Smaller (d4/d6/d8) wedge-style ones are easier to throw for specific numbers than normal dice. Readily solved by use of dice cups.

Comments:

I find that I like them well enough when used with a dice cup. But when not used with a dice cup, I don't much like them.

Besides, there are other shapes of dice besides the "normal" ones that ARE fair, but sure don't look it... the Gamescience d7 is fair when used with dice towers and/or dice cups, but can easily be thrown for a flat by hand on tables with a tablecloth.

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Because of the nature of the fact the rolling-dice can only roll in two directions (forward an backward), whereas a standard dice "tumbles" in any direction, it may be easier to modify the dice by filing a particular edge so it's wider than others...

I'm not talking from personal experience, as I have only recently started playing table-top RPGs and haven't seen one of these die before, but I'm thinking in practical terms.

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