I've had a rather interesting fascination with fountain pens. The mechanism is a thing of beauty, but my attention was recently caught by a rather insignificant phenomenon which I've used a lot in my experience with them. That of soaking leftover ink. All the bright folks here who've written with one must know that a fountain pen soaks ink at times(I do this with the leftover ink in the pot cap to dry it up), and this happens till a certain amount has entered the nib(it varies, of course with the tank airspace and possibly other parameters)
I have a vague idea of how it could work:
The four chambers in the jib/nib are built for ink($I_1, I_2 \& I_3$)/air($A_1$) exchange. $A_1$ replenishes the vacuum that would have otherwise formed while the tank got devoid of ink while writing(here $A_1$ does not fill up with ink). Now when I'm soaking some up through $I_1, I_2 \& I_3$, there is no place for air to enter $A_1$ and somehow ink goes up through $A_1$ too alongside $I_1, I_2 \& I_3$(or it opposes the flow). Now, this is where it's all fuzzy for me, assuming what I've put forward is logically true. What phenomenon could cause ink to be pushed through $A_1$?
Is it possibly a minute pressure difference between the tank and where the end of the nib(aka the capillary) is placed, that causes this unprompted flow?
Some clearing up will be appreciated. Thank you:)