Basic Definition of an Artifact, or Enchanted Object: 

A regular object which was so greatly influenced by an act of the person using it, or by the personality of the user, that it inherited a power which similates the user's action at the time. It is possible for everyone to use most of the different artifacts, but some artifacts are more complex and have certain conditions that need to be met with first, such as, using the artifact on a person you dearly care for, or only on injured people, and so on. It is possible to break most artifacts and thus remove their magic, but some either require a certain way, or cannot be broken at all. 

Most artifacts gain their ability at a single, defining moment of the person using it, like making their greatest discovery in life, saving a person, and such. Some can gain their ability after being used many times in the same manner and under the very same condition.

Each object gains both a positive and a negative reaction to it. An example would be John A. Macready's Sunglasses. Upon wearing them, they would gain invisibility to the naked eye, but could still be seen through a camera lens, but after removing them, the wearer would be blind for a period of time which is twice as long as the wearer had the sunglasses on. (Example from the show.)