You'll see in the written bit below that I have this ink in a Kaweco Sport with a Medium nib and a Sheaffer with some kind of medium nib. These pens are very different, but it strikes me that I really should have put it in something with a finer nib to see what it does there. Cest la vie. I don't have any of that sample left aside from what is in the pens. I'll get a bottle soon, and see how 54th Mass likes a fine nib. I did hear that it feels rough in a Lamy EF nib, but I haven't tried it myself. It might be true. It isn't the most lubricated ink out there.
If your pen is a wet one, then this ink is going to look much more like it does from my Sheaffer. It'll be nearly black. The other blue-black that I like is Air Corps, and it has a tendency to get a little caked up if the pen is really wet, and then it will smear even when it's dried. 54th Mass hasn't exhibited that sort of behavior. It will be darker, but it still behaves well.
If the pen is a little more dry, you'll see a more blue color like the one from my Kaweco. It's closer to blue than to black in that pen. Either one is good for me.
I also wrote a short note on the worst paper that I had around. It's one of those little pads of thin paper that you get at a conference or in a hotel room desk. It's not meant for fountain pens, but it will illustrate the way that the ink will act on the worst paper you can find.
This ink is also rumored to be extremely water-proof.
Is it waterproof? Yep. Really waterproof.
Conclusion: Check this ink out. It's pretty great.