The Source
The bone of the beast and the dead — the ogre smiths' material, the reagent of the poison door's set-terms, and the one the world gives back.
The Yield
A body gives a handful; a handful gives a reagent's worth; a reagent's worth gives the terms.
In the Workshop
The bone is the material that crosses the two systems: the smith's reagent and the spell's exchange in the same handful, and the handful is the one the world gives back.
Cost band: apprentice (raw) — reagent-grade at master — on the ladder in The Maker's Hand, the material is the floor, and the floor is the one the mine or the marsh or the tree has to give. Recipes that take it: runecraft, alchemy (set-terms)