What black ink is this?

I highly admire the work of Adrianna Melina (check her out at Sans Regret in Montreal) it’s all so so clean. A detail I really like with her paintings is how her shading almost has a blueish tint to it from what I can see. I’ve seen quite a few tattooers using this in their flash.

Any idea as to what ink it might be? My Winsor and Newton certainly doesn’t have it, it’s more of that standard grey look.