You’ll see Artifact Forges on the Campaign Map: these are unique locations where you can craft your own Artifacts. They also store items and you can access these items from any other Forge location.
Forging itself works by dragging artifacts from your heroes’ inventory into the forge window. There are three slots on the right side, - this is where you put your artifacts, which will be combined into a single new item when you press the forge button. The fourth slot shows you a preview of the item so you can decide whether it’s worth commencing the forge.
The result is randomly calculated, but there are rules that influence outcome. The “Type” slot will determine the type of your future artefact, namely if it’s going to be a weapon, a ring, etc. The “Primary” and “Secondary” slots will influence the attributes of the new item, and all three slots have an effect on how powerful the forged item will be: if you want a really strong item, you have to sacrifice some of your best artifacts. There are no strict rules to this, so feel free to experiment. Once you’re satisfied with the preview, press the Forge button to create the new item. This of course, will destroy the three source items.
You can create unique artifacts in the forge by placing specific items in the forging slots. This usually involves component type items, which can only be used for forging. They cannot be equipped like normal items. Creating unique artifacts is best attempted in the possession of recipe formulas, although it is possible through experimentation and sheer luck.