Gathering brings in the raw goods. Refining makes the common materials from them, and refining a common one again with an additive makes the uncommon ones. Production takes them from there.
Common metal, refined from Copper Ore by Smelting at level 1 (recipe).
One Copper Ingot takes 4 Copper Ore and 1 Chunk of Coal.
Uncommon versions: Bronze Ingot and Constantan Ingot
Refined further into:
Production takes it, or its forms, in 67 Blacksmithing and 6 Carpentry recipes.
What it adds to gear parts made from it: