One of the first questions new fountain pen users have is how ink actually gets into the pen — and why some pens use cartridges, others have built-in mechanisms, and some seem to involve eyedroppers. This guide explains every filling system clearly, with honest assessments of the advantages and disadvantages of each.
Cartridges
The simplest filling system. A sealed, pre-filled plastic tube of ink clicks into the pen's grip section; a small stopper is punctured when the cartridge is pushed home, and ink flows into the feed. Remove the empty cartridge; insert a new one. No technique required, no bottles needed, no spillage risk.
Disadvantages: cartridges come in fewer colours than bottled inks, are more expensive per millilitre in the long run, and many brands use proprietary formats that can't be swapped between manufacturers. Pilot cartridges only fit Pilot pens; Sailor cartridges only fit Sailor pens. Standard International cartridges fit many European pens (LAMY, Kaweco, and others) — a more versatile format.
Best for: Beginners, portability, travel, and anyone who doesn't want to manage ink bottles.
Converters
A converter is a cartridge-shaped device that replaces the cartridge and allows you to fill from a bottled ink. Most converters use a piston mechanism — twist a knob to extend the piston, dip the nib in ink, twist to retract and draw ink in. Squeeze converters (two metal press-bars to compress and release) are simpler but draw less ink per cycle.
The converter gives you access to the full range of bottled fountain pen inks — hundreds of colours from dozens of brands — while keeping the pen's simple cartridge-based design. Most cartridge-compatible pens also accept a compatible converter. Converters are proprietary like cartridges — Pilot converters only fit Pilot pens.
Best for: Writers who want ink variety without upgrading to a built-in filling mechanism.
Piston filling
A piston mechanism is built directly into the barrel. Twisting a knob at the end extends and retracts a piston inside a sealed barrel, drawing ink directly from a bottle. The entire barrel becomes the ink reservoir, giving significantly more capacity than a cartridge or converter — typically 1–1.5ml versus 0.5ml for a converter.
Piston-filling pens cannot use cartridges — you need a bottle of ink. This is a commitment, but the benefits (capacity, ink variety, satisfying ritual) are substantial. TWSBI pens (the ECO and Diamond 580 in particular) are the most widely available piston fillers at accessible price points. The LAMY 2000 and Pelikan Souveräne are more expensive piston-filling pens with strong reputations.
Best for: Heavy writers, ink enthusiasts, and anyone who values large capacity and bottle-only refilling.
Vacuum filling
A plunger mechanism creates a sudden vacuum inside the barrel when pushed down, drawing ink in very rapidly. Fills faster than a piston and typically holds as much or more ink. TWSBI Vac700R and Vac Mini are the most accessible vacuum fillers available.
The vacuum mechanism provides the largest ink capacity of any non-eyedropper system and a satisfying filling experience. The mechanism is slightly more complex than a piston but well-documented and user-serviceable on TWSBI pens.
Best for: Writers who want maximum capacity in a self-contained pen with no bottle dependency during writing.
Eyedropper
The simplest possible filling system: the entire barrel is the ink reservoir, filled directly using an eyedropper, pipette, or syringe. An O-ring and silicone grease on the section threads create a seal to prevent leaking. Capacities of 2ml+ are common — far more than any other system.
Many pens that weren't designed as eyedroppers can be converted — the Kaweco Sport, Platinum Preppy, and other pens with compatible barrel designs are popular conversion candidates. This requires an O-ring kit (inexpensive) and a small amount of silicone grease.
The main disadvantages: "burping" (sudden ink release when pressure in the barrel changes with temperature), leaking if the seal fails, and the need to handle larger ink volumes. Experienced fountain pen users often run at least one eyedropper pen as their dedicated high-capacity option.
Best for: Maximum ink capacity, one specific colour used heavily, or experienced users who want to experiment.
Which to choose
For a first fountain pen: cartridge or converter. Start with the included cartridge; buy a converter when you're ready to explore bottled inks.
For a dedicated daily writer who goes through ink quickly: piston filler (TWSBI ECO or equivalent).
For the highest possible capacity: vacuum filler or eyedropper conversion.
Browse fountain pens of all filling types at The Journal Shop, including converter-compatible pens, piston fillers, and vacuum fillers.
Where to start: browse our fountain pens and fountain-pen-friendly notebooks at The Journal Shop.
