A rollerball pen is a writing utensil that, like the ballpoint pen, delivers the ink by means of a small ball at the tip. In contrast to the oil-based, viscous inks used in ballpoint pens, the water-based inks of the rollerballs have a very low viscosity which makes a light, smoothly gliding writing possible. There are two types of reservoir systems for the ink: free-ink and fibre or wick reservoirs.
In rollerball pens with “free flowing ink” the ink is held in a tank and is forwarded to the writing tip by means of a baffle delivery system and flows evenly onto the paper without any blotches. The baffle system serves to regulate the pressure between the tank and the surroundings thereby working as both the regulator and reservoir and providing a smooth, even flow of ink.
Wick systems store the ink in a capillary reservoir made out of polyester fibres. This system requires a certain amount of space in the barrel and can only be filled to about 70% capacity because otherwise the ink will run out of the tip. Another 30% of the ink remains stuck in the fibre storage compartment in this type of system. The free-ink system, on the other hand, uses up the entire amount of ink and is therefore able to write about twice as long with the same tank size.
A few pieces of information about the term "archival safe": Only pens with archival safe ink should be used to sign checks, credit cards, contracts, bills, etc. This designation is awarded based on tests of the ink on paper in accordance with DIN norms. Three criteria must be met: