Question - re small hole in Caps of vintage fountain pens

[dave321]

many vintage foutain pens have a small ~1mm hole in their caps.

whyis this?

surely this would allow the ink to dry up more quickly ?

i find it very odd and counter intuitive

[inkstainedruth]

I remember reading an old thread where it said that the holes were there in case some small child swallowed the cap -- but that might have just been conjecture on someone's part.

I've also (on occasion) seen holes in the barrels of vintage pens but I don't remember whether I've ever heard a reason for that (it might have something to do with the sac or diaphragms in the barrels on vintage pens like having air flow around outside them in the barrel, but don't quote me on that...).

Ruth Morrisson aka inkstainedruth

[es9]

 

[MidSouthern-Dad]

They are called breather holes. When you uncap, if there were no such holes, sometimes ink would be drawn out through the nib by the vacuum created by removing the cap.  That would end up inside the cap, or on the section and eventually on your fingers.
The breather hole is placed below the inner cap. The inner cap keeps your nib from drying out.  As you start to uncap, the seal between the section and the inner cap is broken, and air enters into the inside of the inner cap through the breather hole.  This equalizes the air pressure inside and outside of the cap, hence no ink movement.

 

Modern feeds with a lot of fins to collect spilled ink may not need the breather hole.  But, pens with simpler ebonite feeds with few or no fins to act as ink collectors may benefit.  For this reason, many Indian pens with ebonite feeds still feature the breather holes to this day.

[mke]

It has been all said but Gemini makes a good summary - see below. If you add then the information from @MidSouthern-Dad about the geometry and the mechanism, you know everything.

 

The small hole found in the caps of many vintage fountain pens primarily serves to equalize air pressure during uncapping and to prevent ink leaks caused by this pressure change.

 

Pressure Equalization:
When you uncap a pen, a pressure difference can occur between the inside of the cap and the outside air. Without a hole, this pressure difference could create a vacuum, potentially drawing ink out of the pen's nib and feed, leading to messy leaks. The small hole allows air to flow in and out, balancing the pressure and preventing this issue.
Historical Context:
Older fountain pens, particularly those from the early to mid-20th century, often had less sophisticated ink feed systems. These systems were more susceptible to ink flow problems caused by pressure variations. Therefore, the cap hole was a crucial design feature.
Modern fountain pens often incorporate improved feed systems that better regulate ink flow. As a result, the need for cap holes has diminished, although some manufacturers still include them.
Safety Considerations:
It is important to note that with other types of pens, like ball point pens, that the hole in the cap has been standardized as a safety feature to reduce the risk of asphyxiation if the cap is swallowed. This is a separate reason than the pressure equalization in vintage fountain pens.