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After a while, a ball point pen doesn't write very well anymore. It will write for a little distance, then leave a gap, then maybe write in little streaks, then maybe write properly again. It seems to be worse with older pens, but I have observed this with new pens right out of the box too.

Experiments I have done:

  • Take the cartridge out and look at the amount of ink. There is still plenty.

  • Inspect the ball with a jewler's loupe, no obvious damage, everything looks smooth and clean.

  • Stored new pens unused tip-down to eliminate gravity slowly pulling the ink from the ball and leaving a air pocket. Some of the pens exhibit the symptom even when used the first time with the cap never removed before and stored this way for a year.

  • Stuck a wire in the open end of the ink reservoir to see if maybe the end dried to a hard plug so that new ink couldn't move down as it was removed from the reservoir by writing. I have never found anything hard, and observed the same symptoms even after "stirring" the top of the reservoir with a wire a little.

  • When a pen stops writing, shake it hard, like resetting a fever thermometer. That seems to help for a brief while, but so does just waiting a few seconds, so I'm not sure the shaking is relevant.

  • Stored a pen ball-down in a glass of water overnight. The thought was if the ink just above the ball had dried, maybe this would re-constitute it. Some ink clearly dissolved in the water since it was colored, but once the pen was started up again there was no apparent change to the symptoms.

  • Cold seems to exaggerate the symptoms, but warming to body temperature doesn't fix them.

This is not just a single pen or a single model. I have bunch of different pens of different models that do this. I'm curious, what causes this?

Added:

I have done some more experimenting, and it seems Emile Jetzer was right. The cause seems to be that the ink is so viscous that new ink doesn't flow down to replace what is removed via the ball fast enough. Two experiments support this hypothesis:

  1. A pen will write again after a while by just letting it sit ball-down, but the time is significantly decreased when you shake it, like you would resetting a fever thermometer.

  2. Some stick pens are sealed except for a small air hole at the top. Putting lips around the top of the pen and applying pressure as if you were trying to blow into it resets the writing action quickly. Even better, I can write with such pens much longer than they would normally go by holding my mouth over the top and applying constant air pressure.

So, I think the mystery is solved. Probably ink in the reservoir dries out slowly over time by losing water vapor from the top. That makes the entire ink more visous, which explains why old but unused pens also exhibit this symptom.

The next experiment is to take such a pen and add a little water at the top of the ink reservoir, then let it stand for a week and see what difference that makes.

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I think this is the definition of "shows research effort." –  Michael Brown Feb 12 '13 at 0:27
    
Same reason that water on a window form droplets? Ie no constant layer of water. Just throwing this in there. –  user1708 Feb 12 '13 at 18:00
    
I am curious what the relation is between the price of the ballpoint pen and this effect. Some of the cheaper ones (that you get for free on whatever occcasion), don't work at all, and the more expensive (in relative terms), work without any problems. That's my experience. –  Bernhard Feb 15 '13 at 6:33
    
It would be interesting to take a syringe or a similar tool, and apply a strong vacuum to the ball-end of the pen. I wonder if there is a small air-bubble in the ink supply, and that is impeding the ink-flow (kind of like an air embolism). –  Fake Name Feb 15 '13 at 10:42
    
@Bernhard: Yes, these are all probably cheaper pens. Perhaps fixing this problem add manufacturing cost. Getting another pen or a better one is easy enough. I'm curious what the mechanism is. Put another way, if expensive pens don't have this problem, what exactly is it about them that prevents it? –  Olin Lathrop Feb 16 '13 at 14:40
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4 Answers 4

up vote 5 down vote accepted

I would guess it's in part because of the viscosity of the ink. That would explain why the efect is more seen when it's colder. I don't know how doable it is, but you could try filling an ink cartridge with ink used for fountain pens, which is typically less viscous. You might get blotches of ink, but my guess is you won't get dry strokes. So maybe ink manufacturers used easy-flowing ink in ballpoints at first, but then saw it flowed too easily, and made more viscous inks. But this is speculative.

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So you're actually claiming that it is a feature, not a bug? :) –  Bernhard Feb 15 '13 at 6:35
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I'm claiming it's a bug due to an earlier bu fix. As in, it's better to hav a pen that stops writing some of the time than a pen that leaks all of the time. –  Émile Jetzer Feb 16 '13 at 12:51
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I guess this explanation is reasonably consistant with the observed symptoms. It's been 5 days and this is the only real answer, so I accepted it. If someone comes along that actually knows, I'd still be interested to hear. Somebody has to design these things and probably knows all about the failure mechanism and design tradeoffs. Apparently none of them visit physics.se though. –  Olin Lathrop Feb 16 '13 at 14:44
    
I suggest asking on Quora. –  Émile Jetzer Feb 18 '13 at 0:03
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Air behind the ball will do it. Get a good pen and write upsidedown and it will stop writing because the seal is not perfect. Check the ball and socket under a microscope and you may spot the wear on the older pens.

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But how does this explain pens deliberately stored ball-down since new and still exhibiting this symptom? Why does cold exaggerate the symptoms? –  Olin Lathrop Feb 11 '13 at 22:04
    
The air dries out some of the ink and seaps in through the cracks. Cold may exagerate the condition as it shrinks the ink and sucks the air in. –  Jitter Feb 27 '13 at 11:32
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The air dries out some of the ink and seaps in through the cracks. Cold may exagerate the condition as it shrinks the ink and sucks the air in

so pens should be kept with tip in fluid I guess, so no air can come in beside the ball, not water cos it rots, not an evaporating fluid maybe, some oil perhaps, mineral cos bio goes rancid,

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I think it's most likely that you are simply running out of ink and it's hard to tell in a typical pen cartridge. If that isn't it, it's a defect in the ball preventing it from rolling smoothly. You might not see the defect with a loupe.

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No, I checked several of the pens that exhibited this symptom, and they weren't running out of ink. Most have transparent plastic ink tubes, so it's easy to see how much ink is left. I also held them against a light so just in case a thin coating of dry in was left on the inside wall. I could clearly see significant ink remaining. In a couple cases I stuck a wire down the end of the tube and could see and feel it touch the top of the ink reservoir. –  Olin Lathrop Nov 4 '13 at 13:43
    
Then it's got to be that the ball has small imperfections that prevent it from rolling. That's a testable hypothesis-see if the ball rolls when its in this state. –  Richardbernstein Nov 4 '13 at 17:22
    
No, the ball rolls fine. See addition to may answer. Basically, Emile Jetzer was right. –  Olin Lathrop Nov 4 '13 at 20:01
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protected by Qmechanic Nov 4 '13 at 0:47

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