If you’re going to be around fountain pen people, you’re going to realize something real quick: there are a variety of way that pens can obtain and then store ink. Just as a quick little reference, I’m going to list off the most common ones for modern fountain pens.
Usually implied to be of the pre-filled, one-time-use, disposable type, though Noodler’s does sell a pack of what they call 308 cartridges, basically just… reusable empty plastic tubes that can be used to swap out the built in piston filler on their pens with an approximately double the size just.. straight tube.
Almost all cartridge pens can take converters, which.. converts them from taking cartridges to bottled inks, hence the name.
A “converter” is basically just a tube for storing ink with the same interface as a cartridge, so your pen can use the much wider variety in bottled inks. Since all one has to do is, well, fit, they themselves can be filled in a few ways.
Pens without cartridge / converter support usually do not have removable storage or changeable filling mechanisms, you’re stuck with what’s physically part of the pen.
Piston converts have a knob that you twist on the end, which pushes a tiny little piston in and out, and this is what’s used to draw ink into the converter. Kaweko converters are straight piston, meaning instead of turning a cap, you grab the handle and.. push it, you’re grabbing the other end of the piston directly.
The really high-end Pilot converter actually has just a button on the end that you push repeatedly to fill it with ink. Weird, but that’s Pilot for you. Better than trying to turn a tiny little cap, at least.
The “converter” that comes by default with a Pilot Metropolitan is of this type, and there’s a few others following similar lines. They’re basically nothing more than a fancy flexible rubber sac that you squeeze, and when you release, that sucks in ink. Simple and easy to manufacturer, but usually also not transparent, meaning you have no idea what the relative fill level is.
Crescent / Lever
Basically, these pens have the same flexible sac like a squeeze converter, except not only can you not remove it, there’s an external thing on the pen that can be used to compress it.
Crescent filler pens have a round bump that you press in, and lever pens have a lever that you lift. Either way, same thing.
Eyedropper (Literally Just No Mechanism)
So called because they’re commonly filled using.. an eyedropper. An “eyedropper” pen is just one with no filling mechanism and no dedicated ink store, the entire body of the pen itself is where the ink goes, and to fill it you unscrew the grip section, literally just pour more ink in (or, eyedropper it), and screw it back together. Simple, cheap, and effective, usually with massive capacity to size ratios.
Many pens have integrated pistons fillers, and usually the back of the pen body itself is the twist cap, you won’t find a straight piston in a design like this, that’s just way too much space.
Noodler’s pens have an internal removable straight piston that can be removed, either to use their reusable cartridges, or to convert it to an eyedropper pen with a little grease on the body threads.
Oh, these are the fun ones.
Vacuum filling pens work almost on a straight piston concept, except instead of the piston itself doing all the work, as you push the piston down you’re also building a vacuum, so that when it hits the bottom of it’s range of motion, the seal breaks, letting the pen suck up almost an entire fill of ink in about a second. I find them to be the fastest to fill, since about two strokes is enough to get it most of the way there, and I can go from uncapping the ink bottle to re-capping it in about 5 seconds, give or take.
Visconti calls this their “power fill” system, but really it’s just an internal vacuum piston.