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A fountain pen that skips, hard-starts, or suddenly gushes ink can feel mysterious - especially when the nib looks fine and the ink is known to behave well. In many cases, the real culprit is simpler: the converter.
That’s the focus of this video lesson from Kevin at Fountain Pen Revolution. Rather than treating every ink-flow issue as a nib problem, he narrows the diagnosis to one of the most overlooked parts of a cartridge/converter pen: the removable ink reservoir itself.
For fountain pen users, this is a useful shift in mindset. When a pen misbehaves, it’s easy to blame the nib, feed, or ink formula. But converters affect both ink delivery and air exchange - the two systems that determine whether a pen writes dry, writes wet, or stops writing altogether.
In this article, we’ll unpack the key lessons from the video, add practical context, and turn them into a clear troubleshooting framework you can use the next time your pen acts up.
Key Takeaways
- A converter problem can mimic a nib problem. Before adjusting the nib, check whether ink is stuck, airflow is restricted, or the converter connection is loose.
- Bottled ink is usually more economical than cartridges and gives you access to a wider range of colors.
- Different pens require different converters. Standard International is common, but brands like Lamy, Pilot, Platinum, and Kaweco often use proprietary designs.
- Skipping may be caused by ink hanging up at the back of the converter. A gentle flick or advancing a small amount of ink can restore flow.
- Fast writing - especially with flex nibs - can create temporary air-lock behavior. Letting the pen rest briefly may solve the issue.
- Overly wet writing or leaking often points to excess air entering the system. Check whether the converter is fully seated and sealed.
- Threaded converters may benefit from silicone grease on the threads to improve the air seal.
- A simple suction test can reveal a bad converter seal. If the converter doesn’t hold suction, replacement may be necessary.
- Troubleshooting works best in sequence: check seating, ink position, airflow, and seal integrity before assuming a more serious defect.
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Why Converters Matter More Than Many Writers Realize
A converter is, at its core, a refillable mechanism that lets a cartridge-compatible fountain pen use bottled ink. That sounds straightforward, but its role is more important than it appears.
The converter is not just a container. It also participates in the pen’s pressure balance. Fountain pens work because ink moves forward while air moves back into the reservoir. If either side of that exchange is interrupted, the pen’s performance changes immediately.
That’s why converter issues show up in two opposite ways:
- Too little ink flow: skipping, hard starts, railroading, or dry writing
- Too much ink flow: leaking, drips, blobbing, or unexpectedly wet lines
This is one of the most helpful insights from the video: when your pen misbehaves, think of the nib and converter as part of the same system.
A Quick Primer on Converter Types
Before troubleshooting, it helps to confirm that you’re using the correct converter in the first place.
Standard International
The video identifies Standard International as the most widely used format, with a 2.4 mm opening. Many brands accept this style, which makes it a practical default for a lot of cartridge/converter pens.
Proprietary Converters
Several brands use their own fittings and filling designs. The video mentions:
- Lamy: requires a Lamy-specific converter
- Pilot: uses proprietary designs, including push-button and twist-fill styles
- Platinum: requires a Platinum-compatible converter
- Kaweco Sport: often uses a shorter converter due to the compact body size
Threaded Converters
Some pens use converters that screw into the section rather than simply friction-fit into place. The video notes that certain FPR pens use this system.
This matters because a poor fit - whether too loose, too short, or the wrong standard entirely - can create exactly the kind of airflow problems that users often mistake for feed trouble.
Why Many Enthusiasts Prefer Converters Over Cartridges
Although the video is mainly about troubleshooting, it also outlines why converters remain so popular.
1. Better ink value
The economic case is strong. Bottled ink usually provides far more volume for the same price than cartridges. For anyone who writes regularly, this lowers long-term cost significantly.
2. Far more color choices
Cartridge options are often limited. Bottled ink opens up a much wider palette, which matters to enthusiasts who enjoy matching inks to paper, mood, season, or pen.
3. Easier flow management
A converter gives you more control. If a pen begins to write dry, you can manually advance a tiny amount of ink. That kind of quick intervention isn’t usually possible with a sealed cartridge.
4. Helpful during cleaning and filling
As the video points out, drawing ink through the pen also moves liquid through the feed. While this is not a substitute for proper cleaning, it can help keep the ink path active.
That said, converters are not automatically "better" in every way. They also introduce more variables: fit, seals, moving pistons, and potential air leaks. That’s why knowing how to troubleshoot them is so valuable.
When a Converter-Filled Pen Writes Too Dry
Let’s start with the most common complaint: the pen has ink, but the line is faint, inconsistent, or broken.
Check whether the ink is stuck in the back of the converter
This is one of the simplest fixes in the video and one of the easiest to overlook.
Sometimes ink clings to the rear of the converter instead of moving toward the feed. When that happens, the pen may technically be filled but practically starved.
What to do
- Unscrew the barrel and inspect the converter
- Look for a gap between the ink and the front of the converter
- If ink is hanging back, give the pen a gentle flick
- You can also advance a small amount of ink using the converter mechanism
This is a good example of how fountain pen problems can be mechanical rather than mystical. No nib smoothing, feed heat-setting, or ink swapping may be necessary.
Use the nib slit to encourage flow
The speaker also mentions rubbing a finger along the nib slit to help restart flow. In practical terms, this can help encourage ink movement at the nib face.
Be gentle here. The goal is not to bend or press on the nib, only to help surface ink re-establish continuity.
Understand the purpose of agitators
Some converters include a spring, ball, or similar insert to keep ink from sticking. The video points to these features as a way to maintain motion in the reservoir.
This is especially useful with inks that cling more readily to plastic walls. If your converter lacks an agitator and you frequently see ink hanging up, the converter design itself may be part of the issue.
Air Lock and "Breathing" Problems
Another especially useful point in the video is the explanation of air lock.
A fountain pen does not simply dump ink forward. It must also admit air in a controlled way. If ink leaves faster than air can return, the pen may struggle to keep writing.
This matters most with flex writing
The video specifically notes that fast writing - particularly with a flex pen - can trigger this problem. That makes sense. Flex use often demands heavier ink delivery, so the pen’s air exchange system is under more stress.
Signs of temporary air-lock behavior
You may notice:
- good flow at first, then sudden fading
- railroading during flex strokes
- recovery after a pause
- improved flow after manually advancing ink
What to do
- Pause and let the pen rest briefly
- Reduce writing speed if you’re pushing the pen hard
- Advance a very small amount of ink if needed
This is an important diagnostic distinction: if the pen recovers after a pause, the issue may not be clogging at all. It may simply be that the reservoir-feed-air system is trying to catch up.
When the Pen Writes Too Wet or Leaks
Dryness gets most of the attention, but excessive flow is just as frustrating. If your converter-filled pen drips, blobs, or lays down more ink than expected, the video suggests focusing on air intrusion.
As Kevin explains, fountain pens "breathe." In practical terms, if too much air enters the system, too much ink often follows.
Step 1: Make sure the converter is fully seated
A converter that isn’t pressed firmly into the section can allow extra air to slip in. Even a small gap matters.
What to check
- Remove the barrel
- Inspect the junction between converter and section
- Look for visible space or looseness
- Press the converter in securely if the design is friction-fit
This should be one of the first checks for any suddenly over-wet pen.
Step 2: Check for a loose or worn fit
The video also shows a case where the converter is so loose that it falls out easily. At that point, the issue is not user error but hardware wear or incompatibility.
A loose fit can cause:
- inconsistent flow
- leakage into the barrel
- burping
- sudden oversaturation at the nib
If the converter does not stay firmly attached, replacement is often the cleanest solution.
Step 3: Seal threaded converters with silicone grease
For threaded converter systems, the video recommends a small amount of silicone grease on the threads. This is a smart maintenance step because threaded joints can still admit air if the seal is imperfect.
Important note
Use only a very small amount. Too much grease creates mess without improving function. The goal is a better seal, not lubrication for speed.
This advice is especially useful because it extends beyond one brand or pen. Any threaded ink-contact joint can potentially benefit from proper sealing if air leakage is suspected.
The "Bubble Test" and Suction Test Explained
One of the most memorable parts of the video is the simple test for converter integrity.
The method is straightforward: place the converter opening against a moistened fingertip, operate the mechanism, and check whether it creates and holds suction. If it grips the finger or releases with a noticeable pop, the seal is likely intact.
Why this test works
A converter depends on a good internal seal to create pressure changes. If it cannot form suction against a closed surface, it may also struggle to regulate ink and air properly in the pen.
What a failed test suggests
- worn piston seal
- hairline damage in the converter body
- poor assembly
- age-related material failure
In other words, the problem may not be the pen at all - it may simply be a defective converter.
A Practical Troubleshooting Sequence
The video is most useful when turned into a repeatable process. Here’s a streamlined order of operations based on its advice.
If your pen is skipping or writing dry
-
Check the ink position in the converter
See whether ink is stuck away from the feed. -
Flick the converter gently
Encourage ink to move forward. -
Advance a small amount of ink
Prime the feed without flooding it. -
Consider your writing pace
If you’re using flex or writing quickly, allow the pen to rest. -
Inspect the converter type and fit
Confirm that the converter is appropriate for the pen and connected securely.
If your pen is overly wet or leaking
- Check whether the converter is fully seated
- Inspect for looseness or poor fit
- Seal threaded connections if applicable
- Test the converter for suction
- Replace the converter if the seal is compromised
This sequence is efficient because it starts with the least invasive fixes and only moves toward replacement if simpler causes are ruled out.
What the Video Does Well - and What It Leaves Unsaid
The strength of the video is its focus. It does not try to solve every fountain pen problem. Instead, it isolates the converter as a specific troubleshooting target, which makes the advice more actionable.
That said, a few boundaries are worth keeping in mind.
What the video clearly covers
- converter function
- common converter types
- causes of dry flow related to ink position and air lock
- causes of wet flow related to seal failure and excess air
- a quick physical test for converter health
What is not specified in the video
- detailed cleaning procedures for feeds and nibs
- how paper choice affects perceived flow
- whether certain ink properties worsen converter hang-up
- long-term maintenance intervals for converter replacement
Those omissions are not flaws - they simply define the scope. If your pen still misbehaves after checking the converter, the problem may lie elsewhere in the nib, feed, ink, or paper combination.
A More Useful Way to Think About Fountain Pen Flow
One of the best takeaways from this video is conceptual: stop seeing fountain pen flow as "just a nib issue."
A converter-filled pen is a small fluid system with three interacting elements:
- ink supply
- air return
- seal integrity
When one of these fails, the symptoms can look dramatic, but the fix may be very simple. A flick, a reseated converter, a touch of silicone grease, or a replacement converter can often solve what seems like a much larger problem.
For beginners, that’s reassuring. For experienced users, it’s a reminder not to overlook the basics.
Final Thoughts
Converter issues sit in an awkward middle ground: too minor to seem important, but critical enough to disrupt the entire writing experience. That’s why this video’s troubleshooting approach is so effective.
If your fountain pen skips, railroads, blobs, or leaks, the converter deserves an early inspection. Check whether the ink is actually reaching the feed. Check whether the pen is getting the air it needs. Check whether the connection is tight and the seal is sound.
In many cases, restoring reliable ink flow is less about pen repair and more about understanding how the converter manages pressure, movement, and fit. Once you start diagnosing those three things, a lot of "mystery" fountain pen behavior becomes much easier to fix.
Source: "The "Bubble Test" That Explains Most Converter Ink Flow Problems" - Fountain Pen Revolution, YouTube, Jul 28, 2026 - https://www.youtube.com/watch?v=mjpUxuRgZ0M