Fountain pen ink is mostly water. That surprises people. The colour you see comes from a small percentage of dye, and everything else in the bottle is there to make that dye behave once it’s sitting in a narrow feed for months on end.
What is fountain pen ink made of
Nearly all fountain pen inks use dyes rather than pigments. Dyes dissolve completely, so there’s nothing solid to settle in the feed and clog things up. That’s the whole reason your pen writes rather than sputtering to a halt. India ink and most drawing inks use suspended pigment particles instead, which is exactly why you should never put them in a fountain pen.
The water is usually deionised, so there are no minerals to interfere with the chemistry. After the dye, you get a few additives doing specific jobs. Glycerol or a similar humectant slows down drying at the nib. A surfactant lowers the surface tension so the ink wets the feed properly and lays down evenly on paper.Leave a bottle of dye and water in a warm cupboard without one and you’ll grow something. I’ve seen the grey fuzz on a neglected bottle of ink. Not pretty.
Making a batch
The process is fairly ordinary. Dye and additives get weighed and stirred into warm water until the lot dissolves. Then the batch is filtered, often more than once, because a single undissolved speck can block an extra fine nib. Colour and flow get checked against a reference sample, the pH is measured, and if it matches, it goes into bottles.
Scale is the main difference between makers. Big brand operations run this on real production equipment. A one-person outfit might mix a batch in something closer to a large kitchen.
Iron gall and pigmented inks are a different animal. Iron gall actually darkens through a chemical reaction on the page, which is a story worth its own post. But the ordinary bottle of ink on your desk? Water, a bit of dye, and a few things keeping it looking good for years.
Looking for inks
You are in the right place as we have plenty for you, see our fountain pen inks and refills page. The latest addition as of July 2026 is the new Stilform TILT Bottled Fountain Pen Ink