"I have witnessed the explosion of a thousand suns, the extinction of a thousand worlds, the damnation of a thousand souls. I have tasted true power, unvarnished, undiluted, pure—Dark Magic birthed unto Humanity with the cry of our dying world. Whilst you dabble with but a single Wind, I have mastered them all. Fear me, for I am thy better.
"It’s quite simple, really. Chaos is magic, and magic is Chaos. Understanding this simple fact will dispel all the delusions to which your small mind still clings. Oh, but what of the Warp magic of the Skaven? Or the magic contained within the Dwarf Runes, or Battle Magic, or the High Magic used by Elves? Fool, these are all Chaos, albeit, in some cases, cunningly disguised, but Chaos all the same. You see, it really doesn’t matter what the caster believes, what values he upholds, for whenever he draws upon the so-called Winds of Magic, he harnesses loosed energy from the Realm of Chaos.
"What about the Winds and Colour Magic? Utterly ridiculous. It’s a lie invented by Teclis and his cronies to keep Humans from understanding the truth of magic. See, the Elves are dying; they devour themselves. Whilst they squat in their towers on that wretched Isle, their righteous kin, the Druchii send wave after wave against them. For you see, Malekith, called the Witch King by his detractors, understood the truth of Dhar, often called Dark Magic, but that is a false term that understates the essence of this energy. He sees the lie, and it disgusts him. The Elf High Mages seek to keep their power to themselves and fear all others. We, as Humans, could learn a lot from Malekith for he alone sees the High Elves for what they are: gutless cowards who live behind falsehoods in a futile attempt to stave off their inevitable extinction.
"So long as we bow to the strictures of the Orders, we will always be slaves to the Elves and their plotting. We must throw off the shackles of deception and lift ourselves, we true masters of magic, out of the ignorance of structure and restrictions to embrace Chaos in its truest form. Until we do so, we will always be weak, and will always be victims of the savage hordes of Chaos. Only through mastery of all the Winds will we ever contain the threat that looms like a spectre in the north."
- —Magreta Gebauer, Black Magister [2a]
The term "Black Magister" is the phrase used by the Imperial Orders of Magic and witch hunters to describe Magisters who either go rogue, turning their backs on the Articles of Imperial Magic, or who knowingly utilise Dark Magic, or both. This is not a common occurrence, but a few Black Magisters are infamous throughout the Empire.
Black Magisters do not have to have embraced the Chaos Gods, nor must they have begun studying the arts of Daemonology or Necromancy. All it takes is for them to flee their Order and refuse to practice and respect its traditions or intentionally and persistently experiment with more than one Wind of Magic at a time. These traitorous acts will earn the Magister the relentless hostility of his prior Order.
Black Magisters know and accept they have disobeyed the Articles of Magic and have broken faith with their Order. They have been instructed from day one as Apprentices that breaking with their Order is the most terrible and illegal act possible and that using Dark Magic is insanely dangerous. These acts are against the spirit and letter of the law and are morally lacking.
So if a Magister takes the rare and extraordinary step of starting to use these malign energies, he would either willingly embrace his new title of Black Magister or reject any title whatsoever. Whatever the case, Black Magisters tend to look down on their old brethren as narrow-minded, misguided fools who willfully hold back from exploring the true nature and power of magic. These renegades tend to look even more starkly on the self-taught whom they consider ignorant and trivial dabblers worthy only of contempt and destruction.
Black Magisters who do not flee their Order and practice their dangerous and illegal arts in secret would be among the most subtle and powerful of all Magisters to be able to do so without being discovered. They would probably need divine or daemonic aid to hide their corruption from their peers if they reside in the College buildings of Altdorf (as was the case with that vilest of all traitors, Egrimm van Horstmann).