Rollerball Pens
Rollerball pens use a low viscosity water based ink and give a writing experience and effect closer to that of a fountain pen than do ball pens, which use a viscous oil based ink. Rollerball pens usually come with a separate cap to stop the ink drying, but 'capless' rollerball refills are now also available, which can be used in retractable pens.
Rollerball pens can also be used with a gel refill which has water based ink, but this time with a thickening agent, which allows pigments to be used, as in paint, rather than dyestuffs, as used in ink.
