Age of the Dragons
All magical items in the world are created by one of two means – either Mana Investiture or Artifacting.
Some items may not reveal all of their powers to a wielder at first. Even the most powerful items in the world may have been lying dormant for centuries, and require time and usage – and possibly even knowledge – to reawaken their full potential.
The art of Mana Investiture was lost during the Age of Winter by all but the Nejail (Sky People). They guard this secret closely, and absolutely refuse to share it with outsiders.
A mage must know the requisite enchanting spells before he begins a Mana Investiture enchantment. Then, he must spend a significant amount of time enchanting the item.
One of the Seven Swords, an artifact item
The other method by which magic items are created is more meta-game than Mana Investiture. In this instance, items that are present during significant events throughout history begin to accumulate power. Artifacting requires no spells, or even knowledge that its happening. Likewise, Artifacts are not restricted to the usual enchantments of invested magic items.
There is nothing to prevent an item from becoming more powerful – an Artifact may be invested, and an invested item may become an artifact. The two systems are wholly compatible.