Black Fire Opal - liquid core
The big problem with the plan was always that it was going to be noisy: you can’t just pull crystals out of the rock in which they’re embedded without a little bit of chiseling, maybe some hammering. That was why you’d brought the wizard: to keep things Quiet, ideally through magic but also through murder if strictly necessary. Now, though, deep in the tunnels where you were pretty sure they were sourcing the magical rocks from, you understand the downside of this solution as the Wizard compels your fighter to hand over the gems just before you all pass out.
Clear resin with a little bit of rainbow holographic micro glitter around a clear liquid core with genuine kyocera black fire opal chips, inked in copper. Video of the d20 in motion here. The liquid in the core is mineral oil, which caused some resin issues, notably small bubbles. These have been repaired on the set without any large remaining flaws. Some of the opal does appear to be adhered to the top faces of some of the dice, particularly the d20. Because these were a test set, they have been discounted for these small flaws. On testing, they seem to roll as balanced as any other dice. I strongly recommend storing them in a dark place, as all resins may yellow with UV exposure over time and it is most apparent on clear dice.
More photos are available on twitter @cipherdice.