Black as black gets for fountain pens
When I first used pigment based inks in fountain pens, I checked often for any effect on ink flow due to clogging. I have had no such problems with Sailor Nano inks. Kiwa-guro is indeed ultra black like traditional calligraphy inks, and risk free in fountain pens! For example, I use it in a Pilot Custom 912 with an FA (falcon flex) gold nib and the effect is wonderful.