Robe of the Archmage

Robe of the Archmage (aka Robe of the Archmagi) is a mage-specific tailored item.

Background
This silk robe comes in three colors, depending on alignment. It can be white (good alignment), gray (neutral) or black (evil). Many of these robes were destroyed when Dalaran fell, but there are still arcanists making them. The robe’s wearer, if an arcanist, gains several powers. Including armor bonuses and magic resistence. If an evil character dons a white robe, she immediately loses power. The reverse is true when a good character dons a black robe. If a good or evil character wears a gray robe, or a neutral character puts on a white or black robe, she loses some power. The loss of power lasts as long as the robes are worn and disappear when the robe is removed.

Source
This item is crafted by tailors with a skill level of 300. Since it is bind on pickup and only wearable by Mages, there's little point in learning the pattern or crafting the robe unless the tailor is also a Mage.

drops off of Firebrand Pyromancers in Blackrock Spire. Its estimated drop rate is 12%.