It is a nano-carbon pigmented black that, like others of its class, is permanent, solvent-resistant/proof, and very well behaved.
When I first got the ink for testing, it was labelled under it's pre-release name of Black 11.40, but having been released it is now called Barrister Black.
On even poorer quality paper (old stock Reflex) there was no bleeding or feathering, so this is a very well behaved ink.
As you can see, it is a deep, solid black, less matt and more glossy than the normal nano-carbon ink like Sailor Kiwaguro. On paper it looks more like Noodler's Heart of Darkness.
I was able to test it by soaking samples in various household solvents, as below.
So, for those of us in Australia who find that Sailor Kiwaguro or Noodler's Black/HOD are too expensive, or for those who want a carbon black ink that has an almost glossy look, this is a good alternative.