[randito]

My favorite fountain pen inks, especially ones that stand up to watercolors:

Platinum Carbon Black, Rohrer & Klingner sketchINK, and any of the De Atramentis Document Inks.

Noodler's ink is fun (especially the Lexington Grey) but not very water resistant in my experience.

[slowmovintarget]

Many of the bulletproof Noodler's Ink inks will "move" in water, but the stuff that is soaked into the paper is absolutely bonded to the cellulose. This means your writing will remain clearly legible. Some of the bulletproof inks do not budge at all once dry.

The thing about them, however, is they are all dye-based inks, so they're generally safe for all modern fountain pens.

The sketchINK series is a pigment-based ink, if memory serves, so better for dip or brush pens. Platinum Carbon Black is a bit special. It's a nano-pigment black ink. Will not budge, and works well in fountain pens. I also hear great things about the Document Inks.

One of these days I'll pick up a few bottles of the different Document inks (which are designed to be mixed with each other). For black ink, though, my heart belongs to Noodler's Ink Heart of Darkness, followed by Dark Matter.

Rohrer & Klingner iron gall inks (Salix and Scabiosa) are on my list as well... one day.