When Smooth Becomes Silent: The Baby's Bottom Problem and the Lost Art of Feedback

A Correction at the Bench

Last week, a reader wrote to me with a familiar complaint. They had purchased a premium fountain pen—a name I won't mention, but one associated with luxury and heritage—and found it unusable. Not because it scratched. Not because it leaked. Because it was too smooth.

The pen skipped. It hesitated on the downstroke. It required constant priming. And yet, when they described the sensation to a local pen shop, the clerk praised the "buttery smoothness" as a sign of quality craftsmanship.

I need to correct this perception. What that reader experienced wasn't quality. It was a manufacturing defect called baby's bottom—and it's become endemic in an era where polish is mistaken for precision.

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The Anatomy of a Failed Nib

Let me take you to the loupe.

A fountain pen nib functions through capillary action—the same physics that draws water up a paper towel. The slit between the tines narrows as it approaches the tipping material, creating a channel that pulls ink from the feed to the page. For this to work reliably, the inner faces of the tipping material must meet the paper at a precise geometry.

Now, examine a nib suffering from baby's bottom. In the hand, it feels glassy—like writing with a ballpoint that happens to use liquid ink. But under magnification, you see the truth: the inner edges of the tipping are rounded inward, creating a convex curve rather than a crisp meeting point. The shape resembles—hence the undignified name—the plump curve of an infant's posterior.

This rounding creates a fatal gap. The ink, following capillary action, reaches the narrowest point between the tines and stops. It cannot bridge the microscopic void to the paper surface. When you write, the first stroke often fails because the nib is literally dry at the contact point. You must press harder, write faster, or return to priming the feed—compensations that defeat the purpose of a precision tool.

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Why Over-Polishing Became the Standard

In the hand, a nib with baby's bottom feels deceptively luxurious. There's no feedback—no texture, no resistance, no voice. For a novice testing pens on coarse paper in a shop, this sensation reads as "premium." It's frictionless. It's fast. It's also broken.

Mind you, I understand the market forces. Manufacturers, particularly those sourcing from certain German nib houses, have leaned into over-polishing as a competitive feature. In a retail environment where pens are tested for thirty seconds on provided paper, the smoothest nib wins the sale. The fact that it skips on Tomoe River, requires pressure on Rhodia, and dries out during the pause between thoughts—these issues emerge only after purchase.

The problem has intensified with the rise of "buttery smooth" as review criteria. I have seen enthusiasts dismiss a perfectly tuned nib as "scratchy" because it provided pencil-like feedback—that gentle tooth that tells you the pen is engaged with the fiber of the page. We have trained ourselves to equate silence with sophistication.

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The Physics of Feedback

A properly tuned nib should sing. Not literally—though I have recorded the audio frequencies of well-aligned tines, and there is a distinct harmonic to a nib in its sweet spot. But the feedback I'm describing is tactile: the slight catch of tipping material against paper fiber that tells your hand, without your eyes, that the line is laying down as intended.

Japanese manufacturers, notably Sailor and Platinum, understand this. Their nibs are ground with intentional micro-texture—what we call "feedback"—precisely to avoid the baby's bottom trap. They prioritize consistent contact over frictionless glide. The result is a nib that never lies to you. If the angle is wrong, you feel it. If the ink is low, you sense the subtle starvation before the skip occurs.

This is not to say all smooth nibs are defective. A well-ground broad nib, properly rounded on the outer faces while maintaining crisp inner geometry, can achieve smoothness without sacrificing capillary integrity. The distinction lies in where the polish is applied. The outer surfaces that touch the paper can be glass-smooth; the inner surfaces that control ink flow must remain precisely angled.

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The Tap Test

If you suspect your nib suffers from baby's bottom, there's a simple diagnostic. I call it the tap test, though gentleness is essential.

Rest the pen, nib down, on a sheet of your standard writing paper—no pressure, just the weight of the instrument itself. Gently tap the barrel, as if coaxing ink down. Then write a slow, deliberate stroke. If the first stroke skips while subsequent strokes flow normally, you likely have a rounded inner profile. The initial tap primes the gap; the writing drains it.

A healthy nib doesn't require priming. The ink is always at the ready, held in suspension by the geometry of the slit, awaiting only the touch of paper to release.

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The Repair: Not for the Impatient

Baby's bottom can be corrected, but it requires surgical precision. The goal is to remove material from the inner faces of the tipping without destroying the outer polish or altering the tine alignment. I use 12,000-grit micromesh, supported on a firm backing, working in figure-eight strokes under a 10x loupe. The objective is to create a crisp inner edge—a "corner" where the ink meets the page—while preserving the outer comfort.

This is not a job for sandpaper. Not for nail files. Not for the "smoothing" tutorials that suggest writing on brown paper bags until the problem resolves itself. Those methods round the outer surfaces further, exacerbating the defect while dulling the nib's character.

In severe cases—when the tipping material itself is insufficient or misshapen—I recommend professional re-tipping. A good nib technician can weld new iridium to the tines and grind them to proper geometry. This costs more than the pen in some cases, which is why I advocate so strenuously for buying from makers who respect nib geometry over retail smoothness.

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The Verdict: A Tool, Not a Toy

A fountain pen with baby's bottom is not a writing instrument. It is a frictionless object that occasionally produces marks if you coerce it. The tragedy is that many owners never identify the problem—they simply assume fountain pens are inherently temperamental, or that they lack the skill to use them properly.

This is wrong.

A well-tuned nib, even an affordable steel one, should start instantly, lay a consistent line at normal writing pressure, and provide enough feedback to keep your hand informed. The "scritch-scratch" should be present but not intrusive—a whisper, not a scream.

If your pen skips on the first stroke, if it requires a heavy hand, if it feels like skating on ice rather than walking on a path—take it to the loupe. Look at the inner faces. You may find that what you've been told is "premium smoothness" is actually a geometry failure, masked by marketing and mistaken for luxury.

The best nibs aren't the ones you can't feel. They're the ones you can trust.

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Current Inking:

• Pen: Sailor Pro Gear Slim (Steel Nib), Fine-Medium (factory ground for moderate feedback)
• Ink: Sailor Shigure (the subtle shading rewards a nib that doesn't skip)
• Paper: Midori MD Cotton (old stock, for testing the tap test on multiple surfaces)

—J.V.