The Line
the anvil-singers (dwarven) — the only line that makes plate that moves
The Recipe
Inputs: Steel, Mithril (for the plate that moves), a year at the anvil Output: Chain Mail at master, Plate at masterwork Time: a season for chain, a lifetime for the plate that moves
The smithing is where the armor ladder earns its name: the rings, the scales, the plate — each tier is a refusal, and the refusal is the one the anvil has to give a year for. The plate that moves is the anvil-singers' signature, and the signature is the one the story remembers.
The recipe is the knowledge, and the knowledge is the one the guild charges for — on the ladder in The Maker's Hand, the recipe is the middle leg: the world gives the material, the maker knows the recipe, and the item is what the maker owes.