I've read a lot of great feedback on this ink and finally got a full bottle myself. So far, the ink has definitely lived up to its reputation of being interesting and well-behaved.
In my search for permanent water-resistant inks, I've looked at a lot of pigment-based inks, and while there are many nice shades available, they tend to look "flat", with no color variation. There can be some amount of shading, but generally there's an extra complexity to dye-based inks that's missing from pigment inks. This ink defies the pattern and presents a complex, more dye-like blue. There is a great amount of shading and even a purple sheen! And of course it's almost entirely water-resistant after fully drying. Thus it's safe for labeling envelopes and any personal as well as professional correspondence. And as a bonus, it writes well even on cheap paper, with no feathering and minimal bleed-through!
Personally I prefer lighter colored inks, and thus I purposefully put the ink into a wider-cursive italic nib pen with a more measured out flow. I gave up a bit of shading, but the beautiful turquoise-leaning blue of Sei-Boku comes through very well. I have also included what the ink would look like with a dip pen as well as with well-known Jinhao X750 pens which have high ink flow (unsurprisingly significantly darker result and with more shading).
Paper towel droplets show no noticeable color division/spread.
Big thumbs up for this ink! If only it cost a bit less. But at least it comes in a 50ml bottle. I would definitely buy a larger size bottle.
Edited by Intensity, 21 October 2017 - 17:40.