Rollerball pen
Roller ball pens or roll pens are pens which use ball point writing mechanisms with water-based liquid or gelled ink, as opposed to the oil-based viscous inks found in ballpoint pens. These less viscous inks, which tend to saturate more deeply and more widely into paper than other types of ink, give roller ball pens their distinctive writing qualities. The writing point is a tiny ball, usually 0.5 or 0.7 mm in diameter, that transfers the ink from the reservoir onto the paper as the pen moves. Advantages. There are two main types of roller ball  pens: liquid ink pens and gel ink pens. The 'liquid-ink' type uses an ink and ink supply system similar to a fountain pen, and they are designed to combine the convenience of a ballpoint pen with the smooth "wet ink" effect of a fountain pen. The 'liquid-ink' type rollerball pens were introduced in 1963 by the Japanese company Ohto. The gel ink type rollerball pens were patented in 1982 by Sakura Color Products. Gel inks usually contain pigments, while liquid inks are limited to dyestuffs, as pigments will sink down in liquid ink (sedimentation). The thickness and suspending  power of gels allows the use of pigments in gelled ink, which yields a greater variety of brighter colors than is possible in liquid ink. Gels also allow for the use of heavier pigments with metallic or glitter effects, or opaque pastel pigments that can be seen on dark surfaces. Liquid ink roller ball pens flow extremely consistently and skip less than gel ink pens do. The lower viscosity of liquid ink increases the likelihood of consistent inking of the ball, whereas the higher viscosity of gel ink produces "skipping", that is, occasional gaps in lines or letters. In comparison  to ballpoint pens, Disadvantages. There are a number of disadvantages inherent to roller ball pens: Standards. The International Organization for Standardization has published standards for roller ball pens: To comply to the ISO 14145-2:1998 documentary use standard the following has to be established by an ISO/IEC 17025 accredited laboratory: Most roller ball refills comply to the ISO 14145-2:1998 standard and are approved for documentary use. Uses. Former MI-6 agent Richard Tomlinson alleges that "Pentel Rolling Writer" roller ball pens were extensively used by SIS agents to produce secret writing (invisible messages) while on missions. The Ohto Model  CB-10F Ceramic Roller Ball Pen was used at the 1990 Economic Summit of Industrialized Nations.