Rarity

Equipment — gear, weapons and tools — can roll above normal quality when it is crafted or dropped. Resources and consumables never do. Rarity is fixed at the moment the item is made and rides with it through every trade, so you can buy a rare piece from another player rather than rolling one yourself.

A higher tier multiplies the item's own bonuses (including the seconds a tool shaves off an action) and makes it last far longer. It is a fraction of a tier, never a substitute for one: an arcane bronze piece sits below the next metal up, on purpose.

The tiers

Tool bonus is the one thing a tool gets beyond the multipliers: a flat bonus to Success, Yield and Luck purely for being rare. A normal tool gets none of it, so chasing a rare pickaxe is worth something on top of its faster timer.