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 leather, refined from Leather with Suet by Tanning at level 30 (recipe).
One Supple Leather takes 4 Animal Hide, 1 Suet, and 6 Curing Salt.
Refined further into:
Production takes it, or its forms, in 94 Tailoring, 28 Blacksmithing, 18 Carpentry, and 1 Alchemy recipes.
What it adds to gear parts made from it: