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.
Uncommon metal, refined from Copper Ingot with Tin Ore by Smelting at level 30 (recipe).
One Bronze Ingot takes 8 Copper Ore, 2 Tin Ore, and 4 Chunk of Coal.
Refined further into:
Production takes it, or its forms, in 72 Blacksmithing, 1 Alchemy, and 2 Carpentry recipes.
What it adds to gear parts made from it: