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?