The Forge is a gameplay mechanic that allows players to “exchange” undesired Untiered (UT) items for others. The Forge was introduced to the Vault in patch 1.3.0.0 on December 16 2020.
Items require varying quantities of common 
, rare 
and legendary 
materials.
These materials are “obtained” by dismantling other untiered items.
Materials cannot be extracted from the item they are a part of; they are a part of the item itself and cannot exist on their own. Because of this, unused materials are not saved nor stored between forges.
Some items may also require marks from the dungeon they drop from.
Items can be roughly sorted into 5 tiers depending on their required materials and forgefire. As a general rule, dismantling items of a given tier will give a third of the materials it would take to forge the item. This also means it takes three items in a given tier to forge an item in the same tier.
S tier items cost 135 , 120 and 45 materials as well as 1560 
.
Dismantling gives 45 , 40 and 15 materials.
A tier items cost 120 and 90 materials as well as 720 .
Dismantling gives 40 and 30 materials.
B tier items cost 90 and 45 materials as well as 400 .
Dismantling gives 30 and 15 materials.
C tier items cost 60 materials as well as 120 .
Dismantling gives 20 and 5 materials.
D tier items cost 45 materials as well as 60 .
Dismantling gives 15 materials.
Ore can be found as a rare drop from enemies, bought from the shop, or (tentatively) a reward for limited-time events and daily logins. There are four qualities of ore: Basic, Greater, Superior, and Paramount, corresponding to the C, B, A, and S tiers respectively.
A single ore can be used in the forging of an item and will give equivalent materials to a UT of its tier, reducing the number of UT items of that tier required to forge an item in said tier to two.
Forging consumes forgefire , which is obtained at a rate of 400 per day or by using Sulfur. A maximum of 1600 forgefire can be accumulated at any given time.
A few forgable items can be forged from the get-go; most other forgable items can only be forged once their respective Blueprint has been found.
Many UTs, such as seasonal/event reskins of existing items and special UT set items, can only be dismantled.
Reskinned UT items will typically grant the same materials as their base item. See here for an exhaustive list of items that may fit into this category.
UT items that don’t have a base item (such as the Agents of Oryx Gear) will grant materials relative to their rarity and power.
Forging introduced and explained by DECA in the 1.3.0.0.0 patch notes
