Fountain Pen Design

Function, Development, Construction and Fabrication

2.10.1 Marukin Eyedropper

First and foremost, I would like to thank Zollinger (username), a member of (… If you go there, you can select the English version).  He generously provided the photos and proofread, tested and checked this page for its correctness.

Most noticeable is the lack of fins of the overflow slits.  To prevent overflow, the fountain pen has a hand-operated shut-off valve.


The feed is completely machined from Ebonite as you can clearly see from the machine marks in photo 3.   In the following, I address the areas marked with red letters in photo 1.


Photo 1 — Marukin Eyedropper – 1934

At location A, the feed is in contact with the nib, and three capillaries are ending there.  Details are shown in photo 2 further down.  The capillaries arrived there through being cut along the bottom of the air-canal, which is at the top of the feed.

In this case, the breather-hole deserves its name and provides its intended purpose.  Many feeds, including mine, have their air-canal at the bottom, for reasons I have talked about in the chapter Application to the Feed.  The nibs attached to them still have a “breather” hole.  About the “breather” hole’s other purpose I have written in the chapter Nib Manufacturing.

B shows one of the hollowed-out sections (the other is vaguely noticeable on the opposite side), which most probably are intended to absorb surplus ink, but it could also compensate for tolerances of the nib shape.  I wonder because there is no actual capillary to assist in emptying these chambers but, most likely, this job could be executed by the narrow tolerance gap between the nib radius and the feed.

At C is a chamfered away section, it allows the air to penetrate from the air-canal into the ink reservoir.

The stub at D sticks into the hole at the end of the section, which opens into the ink reservoir.  It contains two ink capillaries, it is slightly flattened on top, and the larger flattening at the side runs out at C serving as the air inlet into the tank, see details in photo 3.

Front End


Photo 2 — Marukin 1934 – front end

Photo 2 shows the front end at Aphoto 1.  At 1 you see the arrival of the two ink capillaries.  At 2 is a narrow cut, which marks the centre of the feed, used to align the nib with the feed.  At 3 is a third capillary, which runs along the bottom edge of the air-canal, starting at C, photo 1.  This capillary is not connected with the reservoir; its purpose is to facilitate draining the air-canal of surplus ink.  Any ink in the air-canal prevents air from entering into the reservoir.  This method is used to control ink flow.

It is plausible to assume that when the air-canal is somewhat filled which is most of the time, then all three capillaries supply ink to the nib, and the writing will be wetter.

4 shows the hollowed out section at the seat of the nib.  With the green line, I marked the length of contact between the ink supplying capillaries and the nib which in my opinion is quite small which indicates that this fountain pen is a slow starter.

Rear End


Photo 3 — Marukin 1934 – rear end

Photo 3 shows details of the rear end at D.  At 1, you can see the two ink capillaries and the flattened top of the stub.  I am not sure what this is for; above all, I find the capillaries very shallow, maybe, it helps with getting ink out of the reservoir since the dimension is within the range of the capillaries.  The cross-section of the capillaries determines the amount of ink transported.

3 shows the start of the third capillary, the air-canal-drainage-capillary.  In German, this would be all one word.  Don’t you love it?  At 2 is the larger flat section of the stub, and you can see how it runs out into the curved section at C, shown in photo 1.   Here is the trapdoor, the valve, which controls the air inflow to and the ink outflow from the reservoir, subsequently.  Let me point out the machine marks at the curved section and the flat ends of the feed and the stub.


Sketch 1 — Rearview, Feed inside Grip-sectionSketch 1 may look a bit daunting, it will untangle and surely make sense in a minute.  The letters and number relate to the photos from above.  G, the green ring, is the grip section.  F is the outer diameter of the feed.

C1 (light blue) is the cutaway part at the rear end of the cylindrical part of the feed, allowing the air to enter into the reservoir.  C2 is the continuation of C1 which, as a cut-away part of the stub, goes through the hole in the section, again for air to pass.

D (dark blue) is the solid part stub that reaches through the hole in the section into the reservoir.  D1 aims at the two ink capillaries.  D2, the wall of C2, is formed by cutting C1. D2 is the flat part of the stub for the air to enter into the reservoir.  D3 is the capillary in the corner of the air-canal to help drain it.

And finally, X is the width of the air-canal and Z its depth.  That was not too bad?  Yes, the air-canal is not concentric with the section or the nib, but this wouldn’t matter. The reason for this is the position of the capillary D3 and its alignment with D2 which facilitates the cross-over of ink from D2 to D3 if required.

How it works

In most fountain pen constructions where the feed ends with a stub, it reaches through a hole or short pipe into the reservoir. When the ink comes in contact with the stub, the two ink capillaries D1 suck it in.  The air-canal opening C2 is too big for any capillary action and a meniscus forms across the opening, preventing the ink from entering.  Looking at diagram 4 on page Application to the Feed will help you follow my explanation.

As the ink gets drained out from the reservoir, the vacuum in it increases and fights against the capillary force in the ink capillaries.  The increase of vacuum causes the meniscus at C2 to break, and a small bubble of air enters into the reservoir and reduces the vacuum.  Ink can flow again. This presupposes the air-canal to be empty.

If for whatever reasons the air pressure in the reservoir increases (see Temperature and Air-pressure) and surplus ink is pushed into the feed it will be stored in the air-canal.  When ink is needed for writing (or for unfortunate dripping) the ink in the air-canal is used first, when the capillary at D3, which is thinner than D1, helps to empty the air-canal before any ink from the canals D1 is used.

That’s what happens at the rear end.  Regarding overflow slits, I see no reason for not adding a few at least at the front end.  For the front end around the nib, I have to draw another sketch, for which I need to scout for more information because I don’t like guessing.

If some information is missing, let me know.  I am learning as I go.

Above all: Enjoy!


Amadeus W.

20 November 2016

go to Homepage and Content

▲  top