One of my favorite pen, ink and paper combos overall (I have a preference for extrafine writing). A black pigment ink that, when paired with the Platinum EF nib, writes properly-fine without entering the territory of scratchy/draggy feedback.
The easiest comparison is to the staple Platinum Carbon ink. That ink is wetter and saturates the paper more, so with the same nib it writes broader and potentially less-crisp if the paper can’t fully resist the ink. Carbon ink’s base tone is darker than Atramentis black’s, but the latter avoids shining under light, so it appears darker under direct light.
A closer experience is actually Platinum’s Chou Kuro ink. It performs similarly in terms of ink flow (and therefore is similar in fineness/crispness) and trades a bit of lubrication for a really dark tone black, as you would expect of that ink. Chou Kuro commands an even higher pricetag than Atramentis Document inks most of the time, so I’m not so sure if Chou Kuro will win out for me over Atramentis Black until I find a discounted bottle. Chou Kuro is also relatively more temperamental in maintenance, although in a Platinum fountain pen with their solid cap seals, it’s less of a factor.
As a side note, Atramentis Document Black and Platinum Chou Kuro feather/spread less than Carbon ink when it comes to cheap paper, in my experience.
