Best Waterproof Fountain Pen Inks You Need to Try

Waterproof inks can be a scary thing in the fountain pen world. There is always a concern that if you are not daily driving your waterproof inked pen then over time the ink could harden and clog the feed. But, if you like to do line and wash watercolor work or just take notes you need to make sure won't become illegible from a spilt glass of water, waterproof inks are a necessary risk.

Due to these risks, pen people have rules for which pens they will ink up with waterproof ink. For me, as long as the pen is easy to disassemble and clean and in a lower price category, it will probably be inked up with waterproof ink at some point. I do avoid gold nib fountain pens as some waterproof inks are known to be corrosive overtime and eat away at the surface of nibs.

To start with, let's define the terms you will often see in reference to inks that may be helpful as you dive into the world of waterproof inks so that you know what you are looking at when shopping.

What makes these inks above different from a standard fountain pen ink? Most standard fountain pen inks are dye-based and dye-based inks as a rule of thumb are not lightfast long-term nor are they water-resistant meaning if you want your writing or sketches to last, an ink that has some water-resistance is essential.

There are lots of options on the market but as someone who is constantly using different papers, I would always recommend getting a sample before committing to a bottle of waterproof ink. Depending on the sizing* used on the paper, an ink may never dry fully and it is always better to find that out before you are committed to a full bottle or working on something important.

There are hundreds of waterproof, water-resistant or iron-gall inks on the market but to make it simple we are going to look at my top brand choices in 2 categories: basics and color.

Kiwa-guro is the black ink in the line and while it isn’t the blackest ink in the pen world (that award goes to Platinum Chou Kuro) it is a very black ink and I really like the fact that it dries totally matte.

Souboku is the blue-black in the line and I utterly adore the fact that Sailor took their already solid blue-black and released a nearly identical version that is waterproof. The ink shades quite nicely, proving you can have an interesting ink that is still waterproof. It does have some black sheening in swatches but it doesn't seem to appear in writing.

Seiboku is the blue ink in Sailor’s waterproof ink line but it does lean very dark and is sometimes referred to a blue-black depending on where you are shopping. Much like Souboku, this ink shades very nicely in writing, including with smaller nib sizes. Unlike Souboku though, this ink can sheen purple especially when writing with larger nib sizes.

Currently, Octopus Certified Document ink are my pick in the coloured waterproof category These inks are waterproof, permanent, and in compliance with DIN ISO 12757-2 making them perfect for documents that need to be stored long term or for important notes. They also come in 9 colours meaning that if this level of certification is needed for your job you aren't just limited to black and blue. Currently violet is my favourite and frequently in my rotation. [Editor's note: Goldspot does not currently carry Octopus Fluids inks, but may consider to stock them in the future]

Overall

My top pick for my everyday waterproof ink is always Sailor Kiwa-guro simply due to how well it dries on all the different papers I use from MD to watercolor paper. I have had it inked up constantly in a pen since December 2023.

*Note: Sizing is a coating added either internally or externally during the paper making process that changes the absorption rate of the paper. Sizings are frequently things like starches or gelatine but can also be a material like rosin. Because the whole point of paper being sized is to give liquid more time to dry on the page, on occasion you will discover that an ink just won't dry on one paper for whatever reason due to how the ink and sizing interact.