Artifacts are all the weapons and armors you make for your squad.
Right now, Battlesmiths: Blade and Forge has four groups of artifacts:

• Weapons (made in the Forge)
  • Bows
  • Swords
  • Hammers
  • Daggers
  • Magic staves
• Shields (made in the Forge)
• Armors (made in the Workshop)
  • Heavy armor
  • Medium armor
  • Light armor
  • Clothes
• Headwear (made in the Workshop)
  • Heavy helmets
  • Medium helmets
  • Light helmets and bands
  • Cloth hats

To craft an artifact, your Master needs to know its recipe and have the corresponding skill level.