It’s matter from the Nevernever. Think of it as a cellophane filter, only instead of being around a light, it is spread all through the air. That’s why we couldn’t see the light from my amulet, and why the muzzle flash of my gun was so muted. And that’s how we’re going to take them out.— Harry Dresden
It is unlike other kinds of faeire glamour, which can create illusions and alter emotions. Rather, myrk is a conjuration, tangible and physical, which, like all matter from the Nevernever, does actually exist so long as it has the energy required to animate it. As a physical object, it can be blown away with enough air, and as a magical construct it can be cut off from its source of energy or ground out with running water, reverting it back into ectoplasm.
Myrk naturally spreads throughout the air and suppresses light, with only Amoracchius being able to pierce it. It is created or called forth by Hobs, who maintain it in order to blind their prey and protect themselves from light, which burns them and can kill them.
In the series
In Small Favor, numerous Hobs are sent by Mab to the Union Station[Footnote 1] to waylay the Archive, and they call myrk forth during their assault. Harry Dresden activates the station's sprinkler system, creating enough running water to completely ground it out and revert the myrk back to ectoplasm.