Upgrade Material in Demon's Souls.
- Very rare drop from the Black Skeleton hidden behind an illusory wall beyond the Adjudicator Archstone.
- Rare drop from the Black Phantom Black Skeleton shortly before the last Reaper near the end of 4-2 (requires Pure Black World Tendency).
Pure Bladestone is required to upgrade +4 Sharp weapons to +5. It is one of the rarest items in the game.