As the General Election campaign hots up (the vote’s on 6 May), we start an occasional series about the issues that really matter. Beyond mulling over nuanced presentations of taxation and spending cut party policies, voters are trying to fathom profounder issues: What is Paper? Why is a stapler so called? Where do printers go when they die?
A rollerball and a ballpoint pen are in mechanism identical. In both, ink is dispensed at the tip by the rolling action of a very small metal sphere (about 1mm) of brass, steel or tungsten carbide. The difference is in the ink. In ballpoint pens (you may know them as Biros, from a trademark that has become genericised) the ink is very viscous. Rollerballs employ the same dispensing mechanism, but with a more fluid ink, usually a dye solution.
Gel pens are also in this family. In a gel pen the ink is a gel (natch) in which pigments are suspended. Pigments allow for a greater range of colours. Unlike dyes, pigments also reflect light so that pigment-based inks can be applied to dark backgrounds,