Artisans
The artisans improve the gear you find. Open them with the ARTISANS button on the Character page; each one gets a tab when they arrive.
Faber the Smith
Faber raises an item's +level, one step at a time, up to +10. Any item works: worn, in the backpack or in the chest. Each step costs gold and Forge Materials, and the top steps of high-level items also need Seals. A worn item's sheet has an AT THE SMITH button. Crossing into a new look (Tempered, Honed, Masterwork) gets its own little ceremony.
Fed by: 
Forge Materials from the Legion Foundry, Frontier Bastion, Sealed Scriptorium and the Sanctums (a side pay in each), from Hunt kills, and from Old Marcus. 
Seals from the first win of each dungeon stage. Forge Materials only start dropping once Faber is open.
Lucia the Augur
Lucia rolls an item's enchantments. Choose one of the item's two slots or both; one roll costs one Enchantment Playbook and some gold (more for higher-level and rarer items). The new lines land at once, so leave a line you like unselected to keep it. Two slots rolled together never get the same enchantment.
Fed by: 
Enchantment Playbooks from the Sealed Scriptorium. Before it opens (V-3), Playbooks come as an occasional bonus from other dungeon runs, Expedition bosses, guild rewards, the Battle pass and the shop.
Old Marcus the Salvager
Marcus breaks down gear you no longer need into Forge Materials. Higher-level and rarer items give more, and an upgraded item returns part of the Forge that went into it. Quick picks such as WEAKER THAN WORN, ALL LEGENDARY and BELOW LV N clear the backpack in one go; each asks first and shows the yield.
Fed by: your own backpack: every drop you do not wear. He in turn feeds Faber the Smith.
Morta the Soulbinder
Morta gives gear an affinity, or deepens the one it has. The first infusion of an item picks its affinity: a Weapon or Gloves gain "Damage vs" it, a Helmet, Armor or Shield "Resist vs" it. Each further infusion makes the line stronger, up to a cap, and costs a little more Essence and gold.
- RE-ATTUNE switches the item to another affinity and keeps its strength.
- REBIND moves the line onto another item of the same slot, for example when you find a better helmet.
Fed by: 
Essence of each affinity from the four Sanctums. Sanctum gear arrives already attuned. Guild Expedition rewards, the Battle pass and the shop's Essence Phial add more.