Editing Fountain pen (section)

===Proprietary offerings===
[[File:Fountain pen ink cartridges.jpg|thumb|Proprietary cartridges (left to right): Pilot, Parker, Lamy, short standard international (made by Kaweco)]]
Many fountain pen manufacturers have developed their own proprietary cartridges, for example [[The Parker Pen Company|Parker]], [[Lamy]], [[Sheaffer]], [[A. T. Cross Company|Cross]], [[Sailor (pen company)|Sailor]], Platinum, Platignum, [[Waterman pens|Waterman]], and [[Namiki]]. Fountain pens from [[Aurora (pen manufacturer)|Aurora]], [[The Shanghai Hero Pen Company|Hero]], Duke, and Uranus accept the same cartridges and converters that Parker uses and vice versa ([[Lamy]] cartridges, though not officially, are known to interchange with Parker cartridges also). Cartridges of Aurora are slightly different from cartridges by Parker.<ref name="nibs cartridges">{{cite web|title=Fountain Pen Ink Cartridges|url=http://www.nibs.com/fountain-pen-ink-cartridges.htm|website=Nibs|access-date=27 July 2016|archive-date=24 July 2016|archive-url=https://web.archive.org/web/20160724060403/http://www.nibs.com/fountain-pen-ink-cartridges.htm|url-status=live}}</ref>

Corresponding converters to be used instead of such proprietary cartridges are usually made by the same company that made the fountain pen itself. Some very compact fountain pens accept only proprietary cartridges made by the same company that made that pen, such as Sheaffer Agio Compact and Sheaffer Prelude Compact. It is not possible to use a converter in them at all. In such pens the only practical way to use another brand of ink is to fill empty cartridges with bottled ink using a [[syringe]].<ref name="nibs cartridges" />

Standard international cartridges are closed by a small ball, held inside the ink exit hole by glue or by a very thin layer of plastic. When the cartridge is pressed into the pen, a small pin pushes in the ball, which falls inside the cartridge. The Parker and Lamy cartridges do not have such a ball. They are closed by a piece of plastic, which is broken by a sharp pin when inserted in the pen.<ref name="goulet video" />