Gel Ink

In Osaka, Japan, in the late 1970s, an ink company called Sakura wanted two things that don't go together. Thick ink holds rich pigment, but it drags across the page. Thin ink flows, but it soaks into the paper, feathers, and fades. Every pen maker had learned to pick one. Sakura wanted both.

The way out was a strange behavior some materials have. They act solid while they sit still, and turn liquid the moment they move. Ketchup does this. It holds its shape in the bottle, then flows the instant you shake it. If ink could do what ketchup does, it could stay thick in the refill, packed with pigment, and turn thin the instant the ball rolled.

So Sakura's chemists went hunting for something that would turn their ink into a gel. They tried anything with the feel of jelly, agar and egg whites and even grated yam, more than a thousand materials, but they all failed. None of them behaved in a way that would make the writing feel delightful.

One day a researcher named Inoue was flipping through a chemical trade magazine and stopped at an advertisement for xanthan gum, a food additive that thickens jam and instant soup. To almost anyone else, the ad meant nothing. Inoue still remembered that moment years later, the solution, "flashed across my mind," he said.

And so, they mixed it into their ink… and it worked!

Ink made this way is a gel. Inside the refill it is solid, holding heavy pigment in place without settling. The instant the ball rolls, it turns liquid and flows onto the page, dark, with very little smudging, and it doesn't easily wipe away with water. Sakura filed its patent in October 1982, then spent two more years working out how to fill a pen with an ink that turns liquid every time it moves. In 1984 it went on sale in Japan as the Ballsign, the world's first gel pen.

If you went to school in the 1990s, you probably owned one. The silver ink, the glitter, the white pen that wrote on black paper. All of it was this chemistry.

The best idea in the pen aisle came from the food aisle, not quite as tasty, but as important.