A fountain pen that skips, floods, or suddenly feels unreliable can be frustrating - especially when the nib itself may not be the real problem. In many cartridge/converter pens, the issue starts farther back in the filling system. A converter that isn’t feeding ink consistently, sealing properly, or allowing balanced airflow can make even a good pen behave badly.
This article breaks down the core lessons from Bubble Test: Fix Fountain Pen Ink Flow and expands them into a practical troubleshooting guide for fountain pen users. If you use bottled ink in a cartridge/converter pen, understanding how the converter affects ink delivery, airflow, and reliability can save time, money, and unnecessary nib adjustments.
What a Converter Actually Does
A converter is a refillable reservoir that lets a cartridge-compatible fountain pen use bottled ink. Instead of inserting a disposable ink cartridge, you install a converter and draw ink into it through the nib and feed.
That sounds simple, but the converter does more than hold ink. It is also part of the pen’s pressure and airflow system. A fountain pen works because ink moves out while air moves in. If that exchange is interrupted - or if too much air enters - the writing experience changes fast.
That makes the converter one of the first components worth checking when a pen starts to misbehave.
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Why Many Fountain Pen Users Prefer Converters
The video highlights several practical advantages of converters, and they’re worth emphasizing because they explain why so many enthusiasts stick with bottled ink.
1. Better long-term value
Bottled ink usually offers much more ink for the price than cartridges. For anyone who writes regularly, journals daily, or uses broad or flex nibs, the savings add up quickly.
2. Far more color options
If you enjoy trying new inks, converters open the door to a much broader range of shades, properties, and brands. Cartridges are convenient, but bottled ink is where the real variety lives.
3. More control when the pen starts to dry
One underrated benefit of a converter is that you can manually move a small amount of ink forward when flow weakens. That can help restart a pen without fully refilling it or disassembling anything.
4. Filling can help refresh the feed
As the speaker notes, moving ink through the pen during filling can help keep the ink path more active than a simple cartridge swap. It’s not a substitute for cleaning, but it can reduce minor dryness issues.
Not All Converters Are Interchangeable
One of the most useful reminders in the video is that converter compatibility matters. Fountain pen beginners often assume all converters are universal. They aren’t.
Some pens accept standard international converters, while others require proprietary designs. The video mentions examples such as Lamy, Pilot, Platinum, and shorter pens like the Kaweco Sport using their own formats. It also notes that some converters thread into the section rather than simply friction-fit.
Why this matters in practice
A converter that is technically "close enough" but not truly compatible can cause:
- poor sealing
- inconsistent ink flow
- air leaks
- loose fit
- dripping or over-wet writing
If a pen suddenly behaves erratically after a converter swap, compatibility should be one of your first checks.
Key Takeaways
- Check the converter before adjusting the nib when a pen skips or floods.
- Ink stuck at the back of the converter can interrupt flow; a gentle flick may help move it forward.
- Airflow balance matters: too little returning air can starve the feed, while extra air can cause leaks or overly wet writing.
- A loose or poorly seated converter is a common cause of inconsistent performance.
- Some converters include agitators like springs or small balls to keep ink moving.
- Fast writing, especially with flex nibs, can outpace the pen’s ability to rebalance air pressure.
- Threaded converters may benefit from a small amount of silicone grease to improve the seal.
- A simple suction test can reveal a faulty converter seal before you start tuning other parts of the pen.
When a Converter Causes Skipping or Starved Flow
If your pen writes faintly, skips, or stops mid-word, the converter may not be delivering ink smoothly.
Problem 1: Ink is hanging up inside the converter
Sometimes ink clings to the rear of the converter instead of moving down toward the feed. Surface tension can keep the ink from settling where it needs to be.
The video’s first fix is refreshingly simple: gently flick the converter so the ink drops toward the front. In some cases, lightly encouraging flow at the nib can also help restart the path.
This is exactly why some converters contain internal agitators. A spring or small metal balls break surface tension and help the ink keep moving as the reservoir empties.
What this means for users
If your pen writes for a while and then mysteriously dries despite having plenty of ink left, check whether the ink is actually sitting near the feed. A converter can look full and still fail to supply ink properly.
Problem 2: Temporary air lock
The video also points to a common issue with heavy writing sessions: air lock. If ink is leaving the pen faster than replacement air can enter, the system stalls.
This matters most with:
- flex writing
- fast note-taking
- very wet nibs
- feeds being pushed near their limits
In those cases, the pen may simply need a moment to stabilize. Advancing a small amount of ink with the converter can also help restore flow.
A useful broader insight
This is an important distinction for enthusiasts: not every "dry" pen is actually dry by design. Sometimes the feed is fine, the nib is fine, and the real issue is that the reservoir and airflow haven’t caught up to your writing pace.
When a Converter Causes Flooding, Drips, or Overly Wet Writing
A pen that suddenly gushes ink often feels like the opposite of a starving pen, but the underlying principle is related: air management.
As the video explains, fountain pens "breathe." If too much air enters the system, too much ink can leave it.
Problem 3: The converter isn’t fully seated
A converter that isn’t pressed firmly into place can leave a tiny gap. That gap may be enough to admit excess air, which can increase ink output and destabilize flow.
This is one of the easiest fixes:
- Open the pen.
- Check the converter connection.
- Press it securely into the section if it is a friction-fit model.
- Reassemble and test.
It’s a small detail, but in fountain pens, tiny gaps often create outsized problems.
Problem 4: The converter fits too loosely
If the converter slips out easily or wobbles noticeably, the seal may be compromised. In that situation, reseating it may not be enough. The converter itself may simply be worn out or mismatched.
This is a good example of why diagnosis matters. Users sometimes try to solve flooding by changing inks or smoothing the nib, when the actual culprit is a poor mechanical fit behind the section.
Problem 5: Threaded converter leaks
For pens that use threaded converters, the video recommends a small amount of silicone grease on the threads to help seal potential air leaks.
That’s a smart maintenance step, but moderation matters. Use only a tiny amount - enough to support the seal without creating a mess or risking contamination in the ink path.
The "Bubble Test" and Other Simple Converter Checks
One of the most practical parts of the video is the basic seal test for a suspect converter.
The speaker demonstrates placing the converter opening against a moistened fingertip, then operating the mechanism to check suction. If it grips well or releases with a noticeable pop, the seal is probably sound. If it fails to hold suction, the converter may be leaking internally.
Why this test is so useful
It helps isolate the problem quickly.
If the converter cannot maintain suction on its own, then no amount of nib tuning will fully solve the issue. You’re dealing with a failing reservoir seal, not just a writing adjustment.
What this test does not tell you
It does not diagnose every possible pen problem. A converter can pass a suction test and the pen may still have issues caused by:
- dirty feed channels
- problematic ink choice
- nib alignment
- paper fibers in the slit
Those causes were intentionally set aside in the video, and it’s worth keeping that boundary in mind.
A Practical Troubleshooting Sequence
If your converter-filled fountain pen is acting up, here is the most efficient order to check things based on the video’s logic.
If the pen is skipping or writing dry
- Look at ink position in the converter. Is the ink stranded away from the front?
- Gently flick the pen or converter to move the ink downward.
- Advance a very small amount of ink using the converter.
- Pause if you’ve been writing quickly, especially with a flex nib.
- Check whether the converter includes an agitator and whether ink movement seems normal.
- If problems persist, test the converter seal.
If the pen is too wet, drips, or leaks
- Confirm the converter is fully seated.
- Check for looseness or wobble.
- Inspect threaded connections and consider a small dab of silicone grease if appropriate.
- Test the converter for suction loss.
- Replace the converter if the seal appears compromised.
Beginner Mistakes This Video Helps Prevent
The video is especially useful for newer fountain pen users because it corrects several common assumptions.
"If the pen skips, the nib must need work."
Not necessarily. Converter flow interruptions can mimic nib problems.
"If the converter has ink in it, the pen should write."
Not always. Ink location matters, not just ink quantity.
"A wetter pen means better flow."
Too much wetness can signal an air leak, not healthy performance.
"Any converter that fits is fine."
Fit and seal quality matter as much as basic compatibility.
These distinctions are valuable because they reduce the temptation to over-adjust a pen that may only need a better converter connection.
A Few Limits to Keep in Mind
The video stays tightly focused on converter-related issues, which is helpful, but it also means a few things are not specified in the video:
- detailed cleaning procedures
- ink chemistry differences between brands
- nib and feed tuning methods
- long-term converter lifespan expectations
That’s not a weakness - it’s simply the scope. The main takeaway is that converter troubleshooting should come before more invasive changes when the symptoms point to airflow or reservoir problems.
Why This Matters for Fountain Pen Enthusiasts
For pen lovers, converters often feel like a minor accessory compared with nibs, feeds, and inks. In reality, they are a critical part of how a cartridge/converter pen behaves day to day.
A well-matched, properly sealed converter supports:
- stable ink flow
- easier starts
- more predictable wetness
- better use of bottled ink
- fewer false alarms about nib performance
And because converters are relatively inexpensive compared with the pens they serve, they’re also one of the easiest components to overlook.
Conclusion
When a fountain pen writes poorly, the nib gets blamed first. This video makes a strong case for checking the converter instead. Skipping can come from ink hanging up in the reservoir or from temporary air lock. Flooding can come from a loose fit, a poor seal, or excess air entering the system. In both cases, the converter sits at the center of the diagnosis.
The most useful lesson is simple: treat the converter as part of the pen’s writing mechanism, not just its ink container. A quick inspection, a gentle flick, a better seal, or a replacement converter may solve issues that otherwise look much more complicated.
For anyone using bottled ink in a cartridge-compatible fountain pen, that’s a practical skill worth developing.
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