From: MasterOfMagic at 2021-06-16 02:06:45
Hold the black stone up to the light. Let the light pass through it. Is it slightly green? Then it might be yunzi.
If you’re not sure then get a lead test kit like this and test a few stones, even if they’re not yunzi.
No, the black stones are completely 100% opaque. No light shines through them
