Every newcomer to the wonderful world of pen addiction quickly notices that there are wet and dry ballpoint pens (as in “pens with a ball”). Some of these pens are marketed as ballpoints, some as gel pens, some as rollerballs. The distinction the manufacturers make isn’t always clear, Schneider’s “Viscoglide” pens for example are marketed as ballpoints, but don’t use traditional ballpoint ink. Here is what I have learned over the years about different types of ink.
With ballpoints I mean traditional ballpoints like the BIC Cristal. The ink in those pens is of high viscosity, because it is oil-based, which makes the ink waterproof. The color comes from dyes that color the liquid which makes it less resistant to bleach compared to pigment-based ink. This YouTube video about the manufacturing of the BIC Cristal provides a glimpse into ink making.
Rollerballs contain ink of low viscosity, which provides an even color application, very similar to fountain pen ink. Like fountain pen ink it is water-based. In contrast to fountain pen ink the color in most models is not provided by dyes, but by pigments (polymer molecules) suspended in the liquid, which makes the ink waterproof and oftentimes bleach resistant. A prime example of this type of pen is the Uni-ball eye.
Gel inks are, like rollerball inks, water- and (usually) pigment-based. Viscosity-wise they are in between ballpoint and rollerball inks. There are high-viscosity gel inks like Pilot Acroball or Uni-ball Jetstream refills. Some pens marketed as ballpoints use high-viscosity gel ink, like Parker or the before mentioned Schneider refills. Some gel inks are of lower viscosity, for example Pentel’s EnerGel and Pilot’s G2 inks. They feel smoother and produce a more consistent line, but have a longer drying time.
Please note: Statements about waterproofness and bleach-resistance are best taken with a grain of salt, the exact ink composition varies from manufacturer to manufacturer. The consistency of the color application also depends on the paper used. The paper in the picture above is a smoother one, which means that it is coated and provides less friction for the ball to roll than less heavily coated paper, which explains the poor performance of the otherwise very reliable Acroball on the particular paper (Avery Zweckform notizio).