Leaking, Flooding, and Other Such Inconveniences of the Fountain Pen 
by Geoffrey Berliner

    Why do fountain pens leak, flood, dribble, blot and ruin the occasional dry clean only garment?  We've all experienced these and many other flow related quirks of fountain pens. Leaking, in part, contributed to the demise of the fountain pen during the 1950's and beckoned in the age of the ball point pen; the pen that does not leak.  Because flow related problems are complex, I've broken down the causes of these problems, and leaking in 
particular, into two categories: environmental and technological. 
    The functionality of the fountain is based on two principles: capillary attraction and displacement. The fissures in the feed are capillary conduits for ink to flow when necessary and to remain static when the pen is not in use.  Surface tension of the ink against the fissures of the feed prevents the flowing of ink.  When pen point is put to paper the surface tension is breached because the ink has found another conduit for flow, paper, which has 
absorption qualities and, in essence, is drawing the ink out of the pen. 
    This formula is not complete until displacement is present.  The movement of ink from the reservoir, sac, barrel etc...., can not take place unless there is air to replace it.  This is why there is a channel above the ink fissures for the flow of air: and why a breather hole is present in the nib and in some cases in the feed (the Wirt feed is an example of this). 
Capillary attraction of the ink in conjunction of the displacement of ink 
with air is the basis of why the fountain pen operates.    
    A delicate balance exists which allows ink to flow from reservoir, through the feed, to the nib, and finally to paper. Environmental leaking occurs if this balance is interrupted. A good example of this is when a fountain pen leaks on an airplane due to the change of air pressure in the cabin.  Essentially what is happening is the increased pressure is acting on the ink but more so on the air in the reservoir.  This increased pressure forces the ink out of the pen and therefore causes flooding.  It is often 
suggested that a fountain pen be brought onto an air plane either completely full or completely empty to prevent leaking.  Empty for obvious reasons but full because it is believed that the air pressure will not act as severely on liquids as it will on air.  Even a completely full fountain pen can flood due to a sharp increase in air pressure, so I recommend that you empty your pens 
before flying.
    Leaking can also occur environmentally if a pen is left on its side or left point down for an extended period of time.  Desk set pens are notorious for leaking because they are often left in the point down position.  The design of desk sets provides that the pens can be left in a horizontal position, which can also cause some leaking, but more often than not the pens are left upright.  This form or leaking occurs because the weight of the ink is greater than the force of the surface tension provided by capillary attraction and therefore the ink is pushed out of the pen.  
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    A hot humid day can also cause a pen to leak because the heat  expands the ink within the reservoir.  A fountain pen should not be enclosed or sealed in a plastic bag because changes of air pressure within an enclosed environment can cause leaking.  And never shake your pen, especially in anger, because centrifugal forces can cause leaking as well.
    Technological leaking differs from environmental leaking because the balance of flow is thrown off from some aspect of the pen itself not functioning properly, and therefore the problem is internal in nature.  A multitude of technological problems can exist, either individually or in combination, which would cause leakage.
    The feed can be the source of leaking if the fissures are clogged.  While reconditioning your fountain pen be sure that the fissures have been cleaned thoroughly by using an ultrasonic cleaner for up to 15 minutes with a solution of 1/2 409 and 1/2 water.  If the fissures are still clogged then purchase a small fine wire brush to further evacuate the fissures of any debris.
    An excess of air seeping into the reservoir can also cause leaking.  This can occur if the sac is deteriorated to the point where there is a breach in the rubber. Or if the sac is not completely sealed at the point where it is attached to the section.  Also if the nib and feed are not seated properly into the section then air can seep in. Always be sure that a tight fit is maintained and that the nib is positioned correctly on the feed.  Never file 
the inside of the section if the section is too tight for the nib and feed because this will damage the section and create channels for improper ink and air flow.  On Vacumatics, Ink-vue's, and pens of the like be certain that the diaphragm is properly seated and sealed; and thoroughly clean the breather tube.
    Hairline cracks in barrels and sections can also cause leaking.  Check your pen thoroughly around the section and in the threads of the barrel especially on pens that have threaded sections and utilize the barrel itself as the reservoir.  
    Another aspect of leaking to be aware of is the wettability factor.  This factor insures that the ink will take to the  fissures of the feed.  If the ink does not properly nest into the fissures then two things can occur: first the ink can slide over the fissures and cause leaking or blotting (this can also happen when the fissures are clogged or if soap is present after cleaning), second, the ink can bead up on the feed and prevent flow altogether.  These two occurrences are common maladies of the injection molded feed of modern fountain pens.  Hard rubber feeds have a much higher 
wettability factor than plastic and therefore generally function better.  
Hard rubber feeds are by far more labor intensive and expensive to manufacture because they need to be machined from a solid block of material.  
 Modern pen manufacturers try to circumvent this problem by giving their injection molded plastic feeds a matte or bumpy surface that will attract the ink more sufficiently.  
    I hope that this article has elucidated some of the causes of leaking.  
There will always be those mystery leaks which seem to appear and disappear for no apparent reason.  This is the eternal mystery of the fountain pen and why we love it so very much.
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