How Does a Fountain Pen Work? The Inner Mechanisms of Pens

Fountain pens can be intimidating to beginners, and they can be a little mysterious even to experienced users. Most of us don’t think all that much about how fountain pens work, only that they do work. We stop and think about how they work when they stop working, mostly. This article is going to focus on how the parts of a fountain pen come together to form a tool that will allow you to write words instead of just dropping blobs of ink on your page. It might be more subtle and maybe more complicated than you think. That also means it’s cooler than you think! Read on for information about the anatomy of fountain pens and how they work. Along the way, we’ll talk about why caps are important, how nibs put ink on a page, and why the feed of your fountain pen is more complicated (and cooler) than you thought.

In the end? It’s all about the “glug!”

How does a Fountain Pen Work?

In the most basic terms, a fountain pen is a shell surrounding some sort of ink reservoir that is connected to a feed and a nib. The feed, nib, and reservoir work together to regulate the ink’s flow so that you make intentional marks and not just messy, beautiful pools of ink. This article is going to go deeper than a typical “Fountain Pen 101” would, but I think everyone will be able to follow along.

The Mechanism Behind Fountain Pens

Our beloved pens come in all sorts of shapes and sizes, and they use a variety of filling mechanisms. I’ll talk more about filling mechanisms below, but all of them have this thing in common:

A fountain pen is a controlled leak.

Unless you’re pointing the pen straight up in the air, the ink in the pen wants to get out, and it wants to take the path of least resistance to do that. The task of the rest of the pen is to create a situation where that ink reliably escapes where, when, and how we want it to.

In the next section, we’re going to dive into the anatomy of the fountain pen, and de-mystify that process. Along the way, we’re going to talk about capillary action, adhesion, cohesion, air exchange, unsteady flow, milk jugs, and glugs. Get ready!

The Anatomy of a Fountain Pen

The Body of the Pen

Let’s start with the outer body of the pen. This is the part you see the most often. It’s probably a good part of the reason that you bought your pen. It looks cool, pretty, stylish, futuristic, rustic, or understated and elegant, but it's not really related to how the pen puts ink on the paper.

Well, not quite. Sometimes the barrel of the pen is just a decorative holder for the important systems inside, but other times, it does serve some important functions. Some ink reservoir systems incorporate the barrel of the pen into the function of the pen. Eye Dropper pens can be like this. In this style of pen, the ink reservoir is the barrel of the pen, and so it makes a difference. We’ll cover the link between ink reservoirs and a pen’s performance soon, so I don’t want to give away too much yet.

The Grip Section

This is the section of the pen that you grip. I always feel like this should have a fancier name, but it doesn’t. Most of the time folks in the fountain pen community will just call it “the section.” The section might be part of the barrel of the pen, or it might be separate and screwed into the barrel. Either way, the function is ergonomic. It should be comfortable to hold, and it should make it easy to control the pen as you move it through the motions of making marks.

To accomplish this, pen designers will use different materials (metals, plastics, rubbers, woods, and more), different textures (smooth, polished, brushed, stippled, grooved, knurled, and more), and different shapes (convex like a bulge, concave like an hourglass, wavy, ribbed, curved like a saddle, etc). We all have different preferences, but we need to hold on to something: the section.

The Cap

This part of the pen is pretty important. The cap needs to do several things:

  • It needs to stay on the pen when you want it to

  • It needs to come off when you want it to

  • It needs to maintain a good seal so that leaks are contained

  • It needs to create an environment where the ink doesn’t dry out too quickly.

Accomplishing all of that while looking attractive on the barrel, and probably incorporating a clip or a rollstop, needs some consideration. Some pens are snap-caps that use a subtle clip on the interior of the cap to engage with something on the section or body of the pen. Some are magnetic, replacing the clipping mechanism with magnets. Some are slip-caps that ditch the retainers and magnets in favor of good old friction. Others use threaded caps that screw on in some way. Figuring out what sorts of threads to use and how many is a balancing act, just like figuring out how tight to make the slip cap, because that third function is to maintain a good seal. Too few threads, or too loose a connection, can let ink out when there’s a leak. If ink can get out, then air can get in, and that’s where the fourth part comes into play.

As we’ll discuss below, a fountain pen nib needs to be wet, but not too wet, to function properly. If you’re letting air into the cap, then you’re allowing ink to evaporate at a greater rate than it should, and that leads to a frustrating situation for the user when their pen dries out between uses. Another factor is how much space there is in a cap.

Ideally, there would be just enough room for the exposed parts of the nib and feed in the cap. The more space there is in the cap, the more air there will be, and that air helps the water in fountain pen ink to evaporate, drying out the nib and feed. One common fix for this is to install an inner cap. This inner cap reduces the amount of air-space in a cap, and assures a tighter fit to the section and so keeps leaks in and air out of the nib’s environment.

Ink Reservoir

Ink reservoirs come in many different types, and that’s why I’ve been using that term instead of terms like “converter,” “ sack,” or “cartridge.” Whichever we’re talking about for a particular pen, this is the part that contains the ink. Some of them hold less ink than others (like most cartridges) or way more (as in an eye dropper pen), but they’re all just holding ink. The amount of ink that they hold does make a difference to how your pen functions, with larger ink reservoirs possibly leading to wetter pens and smaller ones to a drier writing experience. That’s often because there is more ink sitting at the top of the feed in a larger reservoir like an eyedropper, and that ink is exerting more pressure. It’s heavier, and the feed might not be able to slow it down as much as it would when you’re using a cartridge with a much smaller volume of ink.

This won’t always be true, because different feeds might be used for pens that are going to be eyedroppers than for pens that will probably have a cartridge or converter attached to them, but many modern pens are advertised as being able to use all three of these modes, and that’s a tall order.

The Nib & Feed

The nib is the bit of metal that you write with. It has parts as well, and they make a difference to the function of the pen. The shoulders of the nib are the widest part, and they’re not just for looks. Their geometry does some work in determining how the nib will feel. The length of the tines, the thickness of the metal, and the composition of that metal will also contribute to the nib feeling soft, bouncy, flexy, or stiff as a nail. The part you write on is called the tipping, and it is usually made of something that is often called “iridium,” but it doesn’t really contain iridium now.¹ Whatever that material is, it needs to be hard enough for you to write on for years without wearing it down. Nibs also have at least one slit to guide ink flow, and sometimes have a breather hole which helps with the air exchange we’ll talk about later.

The feed is the piece of plastic or ebonite that is underneath the nib. You will see a great variety of different sorts of feeds on pens throughout the years, and they each work a little differently, but they all function to provide ink to the tipping and regulate that controlled leak we talked about earlier. Some materials will make the ink flow greater or lessen it, but all of them are designed to keep it in check so that the leak is just fast enough for you to write with.

How Does Ink Flow in a Fountain Pen?

This is the best part.

I think it’s probably well-known that nibs use capillary action to move ink from the reservoir to the page. Capillary action happens when the forces of adhesion and cohesion work together to move a liquid.² As Lakshminarayanan Mahadevan puts it:

The pores [in the paper] draw in the fluid via capillary – surface tension – forces, while the viscosity resists this motion," he said. "The moving pen drags along the fluid, and again viscous forces resist this. Together they shape the blot, if one hesitates, and the line when one's thoughts flow from the mind to the machine that records them – the pen.³

So, the paper pulls, the ink’s viscosity resists that pull, the nib guides the ink to the page, and the feed…feeds the ink to the tip of the nib. This is a really elegant way to think about the interaction between the pen and the paper. It’s a “competition for the ink between pen and paper.”⁴

But, as another expert I talked with explained,⁵ this is only part of the story. Surely capillary action is working here, but if that were all that was going on you would run out of ink really quickly. You’d use the ink that was near the tip of the nib, and maybe the ink in the feed, but capillary action is a fairly weak force and it won’t do the whole job. We can’t forget about another interaction: The Glug!

Milk Jugs & Unsteady Flow

Think about a milk jug. When you take the cap off of the jug and turn it upside down some of the milk in the jug falls out, but not all of it. It goes “glug!” and then some more milk falls out. That glug is happening because as the milk falls out of the jug, it creates a vacuum in the jug. A sort of bubble at the opening of the jug. When it pops, air is pulled in to fill the space, the pressures are equalized inside and outside the jug, more milk falls out, and the process is repeated. It’s an air-exchange operation.⁶ You get the glug because there is only one hole, and the milk and air have to take turns.


If you were to poke a hole in the jug, then all of the milk would fall out at once because the air would replace the milk at the same rate the milk falls out, and you wouldn't have a glug.

Your ink reservoir works like that milk jug, but on a much smaller scale. As your feed runs lower on ink the reservoir glugs more ink into the feed. When your pen is working well, though, you’re not going to notice this glug. You’re just going to keep writing with a smooth flow of ink instead of having ink falling out onto the page in a “blurp.” And that’s because the feed isn’t just guiding ink down the nib. It’s also regulating the air-exchange between the nib/feed and the ink reservoir.

Different feeds work differently, but the key is that they have different channels for the air and the ink so that about as much air enters the ink reservoir as ink leaves it. The exchange isn’t perfectly smooth, it’s an unsteady flow, but you wouldn’t want it to be perfectly smooth because then all of the ink would fall out. So the pen’s feed is responsible for regulating the rate at which air is exchanged with ink in the reservoir. When the feed is working well, it flattens the glug so much that you aren’t going to notice it, and that’s really clever.

The Cleverness of the Fountain Pen Feed

All of this hidden feed-action is made more impressive when you think about what we’re asking the feed to do. It needs to work pretty much the same way with liquids that contain different dyes, have different pH levels, contain different pigments, contain shimmers, are at different temperatures, AND are contained in different ink reservoirs. The amount of ink in the reservoir makes a big difference to how this unsteady flow operates (because there’s more pressure pressing down when there’s more ink, as in an eyedropper vs a cartridge). The feeds in our pens need to try and regulate the ink flow when the pen is full just as well as when it’s nearly empty, and that’s pretty impressive. Our fountain pen feeds, nibs, and ink systems are keeping all of these forces in balance while we write, and that’s pretty special.

 So, that’s how a fountain pen operates. It is more complicated than we usually think it is, but the core concept is that the fountain pen is always a controlled leak. The cool part is just how that leak is controlled.

Getting Started With Your Fountain Pen


Now that you’ve got a handle on how these cool writing instruments work, you might want to check out some of the other resources that Goldspot has available for you in their magazine archive.

How To Choose Your Fountain Pen

For starters, you'll want to know more about the best fountain pens for beginners. We made it easy by collecting all our top suggestions, including highly-reviewed starter fountain pens our customers enjoy. Once you've settled on a pen design that you feel will be a good fit, select your nib size with confidence using our introductory guide.

How To Fill Your Fountain Pen With Ink

There are lots of different filling systems for fountain pens, and these videos will show you how to fill a bunch of them

How To Write With a Fountain Pen

How To Clean Your Fountain Pen

Cleaning a fountain pen might seem complicated, but it really isn’t. Keeping your writing instruments in good working order is one of the best ways to keep enjoying your pens for years to come.

Special thanks:

I would like to give special thanks to Dr. Nicole Sharp, whose work you can find here, and my other awesome, but confidential, source for the scientific and engineering knowledge they’ve passed down to me. Any mistakes in the explanations are mine, and not theirs.



  3. Ibid.

  4. Ibid.

  5. They’d rather remain anonymous for this article.

  6. (Okay, air is also a fluid, so it’s really a fluid exchange. I’m simplifying some things here.)

About the Author

Mike Matteson is an educator, gardener, and video game player when he isn’t creating stationery content on YouTube, Twitch, or his blog.

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