Keeping that ink all mixed up...

[HedgeMage]

Many Pilot converters contain ball bearings or other small weights which disrupt the surface tension of the ink inside of the converter as the pen is rolled or tilted.  (See photos below, courtesy of JetPens who are awesome.)  I find this extremely helpful with shimmer or high-sheen inks that contain particulate.  It's easier to keep the particulate well-distributed within the ink by manipulating the pen, because the ink can't get "hung up" in one spot and fail to mix.

 

I recently ordered some Faber-Castell converters that use the same technique, and look international standard...we'll find out whether I'm right when they arrive.  However, I'd really like a solution for piston-filling and eyedropper pens.  Does anyone have a favorite object to stick in the ink reservoir of such pens, which breaks the surface tension as described but won't interfere with filling or the ink flow when writing?

 

[LizEF]

Self-fillers (piston, eyedropper, vacuum) usually have a large enough ink chamber that the ink's surface tension can't hold it away from the feed - that's the real use of the agitator - to break the surface tension of dry inks.

 

A secondary purpose is to mix up glitter (and maybe pigmented) ink. But I find the agitator isn't needed for this.  With pigment, I've never needed any kind of agitation (e.g. of Sailor Souboku that lives in my TWSBI Eco full time), and with glitter, I've found that the agitator doesn't eliminate the need for you to rock and roll the pen.

 

In other words, while you might could add an agitator to a self-filler that allows sufficient access to the ink chamber, I don't think you'll need it, and I doubt you'll benefit from it.