Citystate of the Invincible Overlord
Bone iron (sometimes called bone ore) is a whitish, metallic substance, of which it is said that forms on sites of human torment. It is difficult to find, but once one knows how, the material is said to be relatively abundant. Of course, that may just be a grim commentary on suffering.
Rumors have it that weapons formed of bone iron have necromantic properties, or can cause necrotic damage. It can also be distilled into various poisons. These were the discoveries of the Subtle Prince.