Platinum Pigment and Carbon Inks include our favorite waterproof ink, Platinum Carbon Black. This dark pigment ink barely budges under water. If you scrub at it, you can dislodge pigment particles from the fibers of a page, but light pressure with a wet brush has almost no effect, and it holds up to accidental spills or dips with no issues.

An important use case of waterproof inks: art! Some artists enjoy using Platinum Carbon Black with watercolor paints. We don’t necessarily recommend it for quick en plein air painting because the ink requires a few hours to fully “cure,” but you can always draw a scene and paint over it from a reference picture later.

Tautologically, a waterproof ink should be waterproof, but let’s take the time to define our terms. “Waterproof” generally implies total resistance to water, with no fading, blurring, or discoloration at all. This is a tremendously high bar for fountain pen inks to meet because most are dye-based and water soluble. On our website, we’ve defined “waterproof” as unaffected by a dip in water, though dye or pigment may still move around a little with additional force from a wet brush.

“Water-resistant” ink, meanwhile, will either blur in a water dip or smear enough under a brush that it outweighs perfect dip resistance. In either case, lines should remain legible.

There’s a lot to know about inks—so much that we put it at the end of this article, rather than letting you drown in an ocean of ink information right at the start. To quickly summarize, fountain pen inks can be either dye based or pigment based. Overall, most inks are made by dissolving dyes in water, which washes easily out of pens and paper.

In this guide, most inks are pigment based, colored with tiny insoluble chunks of color that snag in paper fibers. Pigment ink calls for a more regular pen cleaning schedule, but is much more durable on the page. We test inks on smooth Rhodia DotPad paper, so our pigment ink recommendations may actually be even more waterproof on toothier paper.

One of the primary joys of fountain pen ink is selecting the perfect color. You don’t need to sacrifice that to enjoy waterproof inks—several of our options encompass the whole rainbow. That said, if you want a waterproof shimmer or metallic ink, fountain pen ink will not be your friend; you’ll need to jump ship to calligraphy ink used with a dip pen.

Most highlighters are markers that use water-based inks, so ink behavior under highlighters can be predicted with how it behaves under a water brush. If you love an ink that’s not water resistant and still want to highlight it, consider a gel highlighter or highlighter pencil. A few inks like Diamine Evergreen can actually be erased by gel highlighters, so be sure to test a writing sample before you highlight anything important.

Put simply: there are some situations where you have to be picky about your ink. Writers who highlight over their words and artists who paint over linework will both have stringent requirements for waterproofness. However, writers who don’t highlight or artists who want to coax a faint ink wash out of their lines may be happy with water-resistant inks instead of strictly waterproof inks.

While intended for use on official documents, De Atramentis Document Inks offer a wide range of colors including bright cyan, magenta, and yellow. You can buy a few bottles and carefully mix your own colors like a printer who’s been granted free will. We did find that these inks feather somewhat, so they’re likely more useful for artistic applications, where feathering will add texture and not necessarily impede legibility at a small scale, than writing. Like many feathering-prone inks, these also dry very quickly. One odd caveat: in black only, this ink did not feather but did lose some waterproofness.

Noodler's Bulletproof Inks are dye-based inks with special chemical formulations that bond to cellulose, making them waterproof without the risk of pigments clogging your pen. They’re also resistant to bleach and UV light. Some inks come with additional features, like Polar inks that resist freezing temperatures. They also have a robust range of colors. The downsides of these inks: high risk of feathering (more dramatic with Polar inks), bottles filled to the very brim that require careful opening, and slight variations in color between batches.

Traditionally used for important documents in some areas of Europe, super-permanent iron gall ink is available across several brands. We prefer Diamine Registrar's Blue-Black Ink, an ultra-dark denim blue that barely budges at all when fully cured. For an option with a more vivid blue that leans towards purple, as well as slightly increased smearing, try Rohrer & Klingner Eisen-Gallus-Tinte Salix (also available in true-purple Scabiosa). Both inks go on the page bright blue and dry down to blue-black, which will certainly keep you entertained as you write. Old-timey iron gall inks were acidic and could eat through paper and corrode pens, but more modern iron gall ink formulations shouldn’t require a more rigorous cleaning schedule than usual.

Kala Nostalgia Inks are nominally water resistant instead of waterproof. Why do we dare recommend them? They keep a legible core of color in their lines when wet, we found that gentle brush pressure dislodges barely any pigment, and we’re bewitched by their dreamy off-gray hues. Artists can use them to create subtle wash effects, adding depth to a drawing without carrying around a full watercolor palette, with no fear of erasing their lines entirely.

Another option are rich Sailor Pigment Inks, which have a simple, classic color range of black and two different blue-blacks. They’re more easily activated by water and smear a little more dramatically than the Kala Nostalgia inks, but remain legible overall.