Fountain Pen Design

Function, Development, Construction and Fabrication

2.9 Feeds Made of Plastic

…and not hard rubber
Some of you may snobbishly wrinkle your noses.  I hear you say: Plastic, cheap stuff …  can’t really work … proper fountain pens have feeds machined from hard rubber, also known as Ebonite (on Wikipedia).

And hearing this comment around me, that’s where I started my research, in 1978.  I had some ideas about how to improve the design of feeds and their function. They were discarded by the experts, condescendingly announcing: “It can’t be done in rubber.” At that time I didn’t have the confidence to oppose, yet.

Mind you, we are going back a few years when CNC machinery was still in its infancy.  Today, everyone has one (a CNC machine centre), just like 3D printers. Could one produce feeds with a 3D printer? Wow!  That’s today. The story I am going to tell you unfolded forty years ago.


What forcefully opened the minds of the experts and started the search for alternatives, was the increase in the cost of machining, even when using turret lathes and other automated machinery.  Employing rubber feeds for fountain pens in the medium range retail price, the profit margin for permitting rubber feeds was almost depleted.

For sales and management, looming dark clouds had crept up, pressing them to unavoidable fundamental decision-making – there were three choices:

1.  Remain true with tradition and continue using machined rubber feeds, which requires focusing on the already dwindling upper market segment and inevitably surrender the midrange market to whoever wants to take it.  The lower segment had already been lost to the Eastern countries.

2.  Produce injection moulded plastic feeds in the form of rubber feeds and fit them in medium market fountain pens. The company would need to accept the consequential, reduced performance.  Inevitable, consumers will notice this, in due course. The company must accept a decline of market share, swallow its pride, suffer to soil the brand name and loss of kudos.

3.  There was this young ingeneer, who had just started with the company and had no idea about writing instruments.  He was confident (based on what?) that he would come up with something to alter the characteristics of moulded plastic feeds so that their function would be equivalent to rubber.  To do this, he wanted a budget and one year.  And what if he could not do it?

How desperate must they have been to still give him a chance with all these doubts?  In the meantime, they haphazardly plodded along with solutions 1 and 2, quietly praying. How else could they find any sleep at night?  I had an idea, but it was too early to talk about it in particular with non-technical people. Furthermore, I also had to learn more about fountain pen functions and inks, and how they were working together.  Honestly, here I was almost at the start of my learning curve, where did the self-confidence come from?  A prerogative of youth?


I have written already about ink surface tension and capillary forces under their particular headings. Knowledge of this matter is a prerequisite for explaining and understanding the content of this chapter.  Therefore, I decided to write about the fundamentals first; otherwise, it would have been too much for me to keep it all in my head and organised on this site.

A recommendation: If the above topics are unfamiliar to you, I strongly suggest that you work through them before you continue here.  I want to stay focused on this topic’s content for your as well as my sake. Writing again about peripheral stuff will disperse our concentration; the subject can be demanding enough as it is.

Roughing it

I had noticed that roughing a nib’s reduces the surface contact angle, making the metal appear/behave more hydrophilic, photo 1, in particular, on the underside, where attractiveness is not required.

nib on holder below

Photo 1— Roughened Nib

How could this happen?  There was no change in material or material characteristics and the material preparation (cleaning) had been the same.

I said: appear!  Since we now know all about surface reaction, we can ask more specifically: “Why does roughing the surface reduce the contact angle?”

Let us look at the contact angle θ.  It describes the angle, which the liquid forms inside itself when it comes in touch with a material of different surface characteristics, with a metal surface, in our case.  For the moment, let’s forget the gas around the couple; it has an effect, too.


Drawing 1 — Contact angle on a smooth surface

In drawing 1, as expected, you see the liquid forming the contact angle θ1 (theta) with a flat plane of the solid surface.

Roughing the surface can be depicted as innumerous, irregular mini-planes forming arbitrary angles with each other and the median plane (red dotted line) as shown in drawing 2.

A drop of liquid responds to those angled mini-planes, not to the median plane.  It does not know of a median plane.  The liquid forms the same contact angle θ1 with all the differently angled mini-planes along the perimeter of the drop.

Drawing 2 — Contact angles on a rough surface

Looking at it from the drop’s point of view, there are regions, where a particular mini-plane rises in regards to the median plane, like on the left side of the drop and there are others, where the mini-plane falls off like on the right side.

On the left side, the apparent contact angle with the flat appearing surface, represented by the median plane is θ2, which is smaller than θ1, due to slope angle  S1.

θ2  =  θ1   –   slope angle S1   

On the right side the slope angle S2 tilts away from the drop curvature, the apparent contact angle θ3 is larger.

θ3  =  θ1  +   slope angle S2

Around the circumference of the drop, it balances out.

It was my deduction: “When the roughing was fine enough, then the surface reaction would change from hydrophobic to hydrophilic.” Where the contact angle is smaller, in this micro-area the liquid behaves as if the material is more hydrophilic and the liquid stretches out. However, in areas of increased contact angles, the liquid’s behaviour should be more hydrophobic.

Is it logical to assume that all around the drop, the larger and smaller contact angles balance each other out? Must I conclude that my hypothesis was false? Let me try to explain it in a way which makes it plausible.

Yes, there are areas forming an increased contact angle and the liquid is confronted with increased resistance to flow.  However, the minuscule areas with reduced contact angle pull on the elastic skin of the liquid and always drag it into regions with a smaller contact angle. Eventually, the drop is surrounded by more hydrophilic sectors and the liquid spreads out, encircles those hydrophobic sections and pulls the liquid across them.

How about that? As we know and evidence demonstrates, roughing a surface cons the liquid into believing the surface of the solid has changed.


Rough surface corner draw

Drawing 3  — Different scratches, different radii

There is an additional effect contributed by capillary action which provides another explanation for the effect of roughing a surface.  Referring back to the chapter on Capillaries: “… the capillary rise depends on the radius of the capillary.”  There, I explained this in diagrams 5 and 6, whereby in squarish capillaries the rise increases in the corners, due to the projected radius reduction.

Returning to here, drawing 3 shows an application of the above.  The roughing has formed arbitrary grooves or scratches. In the drawing, I selected two of them with different inclusive angles, γ1 and γ2.  At the same level (red line), radii R1 and R2 (relevant for the capillary pull) can be drawn, and they are different.  The capillary pull increases inversely proportionally with the radius.  Meaning: with all other parameters the same, but R2 being 4 times R1 the liquid would flow 4 times further in the narrow groove.

In summarising:

1. We have gained knowledge about circumstances, which make a surface behave more water-friendly, hydrophilic, at least in some areas and that’s what counts.

2. Liquids form skins towards gases and solids and their shape and size depend on their specific gravity, surface tension and the surrounding gas.

3. As long as there is a sufficient amount of liquid pulled forward, the rest will follow, even across hurdles of hydrophobia.

As simple as the results of my experiments were, understanding them, having gained a feeling for them, was my first step towards making a plastic surface behave like a machined rubber surface.  The main point I learned was that there is no request for particular material characteristics, but only the ability to alter its friendliness towards the liquid.  Roughing its surface appeared to be the right track. You may say: “Obviously!” but now we know why, and we are confident in our progression, something very important when there is a deadline and you depend on someone else’s money.

To prove my train of thought, I took a piece of machined rubber and polished it at the buffer. Once it was shiny, I made sure to remove all the polishing compounds.  Voilà!  Polished rubber didn’t like ink!  Rough this polished piece, and we are back to normal.

My deductions were:

      1. It is the machining, which causes the micro-scratches and cracks on the surface of the rubber, and they make the rubber hydrophilic.
      2. The reason for rubber being used is tradition.

In the early production of fountain pens, forerunners of plastics (synthetics) were used, amongst which, rubber (Ebonite), was one of the earliest.  For the production of feeds, any other material could be applied as long as it forms micro scratches when machined.

This shows, how attached to tradition we are, to a point where we don’t question.  During my years of apprenticeship and early of ingeneering, I had often asked the older tradesmen about the why and how.  Most often, I heard the stern reply: “We have always done it this way.”

Finding out that polished rubber is hydrophobic by nature, proved my theory, but only half.  For the other half, I would need to demonstrate that roughing plastics (at least some) would improve their water-friendliness.

By the way, ever asked yourself what Ebonite is? It’s a vulcanised natural rubber, originally invented and used as a cheap replacement for ebony wood. Ebonite for feeds and pen components consists of 30-40% sulphur and linseed oil as the rest, something very oily. Who would ever think to use it for producing components which must be absolutely hydrophilic? Are you on my side, now?  Let’s do it!


To begin with, I used sticks of plastic from leftovers (runner and sprue) of injection moulded components of different materials. One guide was their appearance, namely, their mattness and surface hardness because the latter permitted easy matting with sandpaper. My first choice had been polycarbonates, especially the one with up to 30% glass and carbon fibre filling. Further on I selected acetal, a hard and easy machinable plastic, followed by PMMA (polymethylmethacrylate) and polysulfone of similar characteristics.

Then I had ink capillaries cut in them in our existing (then) manufacturing process. Then, the feed’s general shape had been injection moulded, but ink capillaries and overflow slits had been machined into the feed afterwards.

Surface action (wettability and contact angle) and capillary rise are proportional.  Through this correlation measuring the rise of ink gave me comparative results, which was enough for deciding on the efficacy of my experiments and provide me with a selection of suitable plastics.

Surprisingly, my first choice, the mono-polymers didn’t perform that well. The copolymer plastics such as SAN, ABS and SMA showed far superior results. And then it was when luck, Fortuna, had lent a helping hand, unbeknown to me, at the time.

How to Rough it?

Initially, I applied 400 grit wet and dry polishing cloth and went by looks and feel.  At that time I was only investigating the general effect on surface tension behaviour.  Later, I worked with machined capillaries, sometimes several in the same piece of plastic. They were produced on our standard slit cutting machine which, as a final part, included a cleaning process applying high-pressure air blasting and brushing to remove any shavings and the burs along the top edge of the canal.  Whether this was the best way was of no concern to me, but the consistency of standardised machining was.

During one particular test, the results across various plastics had remarkably improved.  That’s when the ingeneer turns into an investigator.  One just does not ignore such facts.  The microscope supplied the answer when I sliced the test pieces along the capillary.

Along the sidewalls of the groove were distinct circular machining marks.  They had been caused by the blade not being correctly aligned with the direction of feeding when machining the test sample.

To prove this finding correct, I went back to wet and dry cloth.  This time, I did not just rub the sample arbitrarily but rubbed it in one direction, meaning, along the axis of a sample stick.  I was right. Mainly, on a flat surface, thus eliminating the effect of gravity, the ink spread faster and farther along with the marks than across the scratches.

This was good news and helped me in getting a feeling for what was going on in the realms of fluid dynamics.


Now, I needed to find a process, which could be applied in a mass-production. Any form of machining, which would require individual component handling, would be too costly, that’s where we were now at, an injection moulded blank with machined capillaries and slits.

I also needed to remind myself that my job was not to find out fabulous things about plastics and surface finishes, to pursue no romantic adventures, as much this would have been my preferred course but merely to lower production cost of the feed.


The simplest solution would have been if the roughness could have been produced during the moulding process.  For this test, I had produced a simple test mould, in which samples (round sticks, ∅6mm × 50mm) were produced.  The surface of the mould cavity was easily exchangeable with other shells with different finishes, such as:

keep as machined (drilled and honed)


roughened through electro-erosion, with varying degrees of roughness

ground, longitudinally, with various coarseness of grit

To cut a long story short, nothing worked.  The samples looked almost the same.  Why?  The microscope revealed it.  The grooves, scratches or markings of the shell cavity showed on the plastic surface to a much lesser degree, and they were all rounded, they didn’t represent the characteristics of the shell’s surface.

The surface tension of the hot, liquid plastics inside the mould was too high to follow the contours of the roughness.

Changing the injection process parameters (pressure, heat, time) affected results only marginally, if at all because they fell within the range of the tolerance of the test equipment.  One could consider this approach as a failure, however when working at the forefront, it is equally vital to know what does not work.  Above all, each bit of knowledge provides more understanding of the investigated field.

At this time, I felt stuck.  Not nice to be there, but I was stuck.  Almost ten years working as an ingeneer had provided me with confidence.  In all my previous jobs, I always had found good solutions.  In moments like this, it feels good to know there is something to rely on, even it is nothing concrete.

Another Way of Roughing

An ingeneer never stops.  We get paid for eight hours a day, but most, if not all the solution finding happens during quiet moments which hardly happen at work but rather at home, on the bus or shopping. At the time  I was playing with my five-year-old daughter.  Someone gave her a plastic toy (I wood not!) and some parts had a metallic finish.

Of course, this was not the first time that I had seen metal coated plastics, but this time it triggered something.  This time I asked and found my next approach.  When nagged by a problem, even subconsciously, the mind must be on special alert.

What is the process of getting a metal finish onto plastic?  Metals have a higher affinity for water than plastics.  What would be wrong with metallising a feed?  Metal coating must be cheap; otherwise, they would not cover toys with it.

How it is done?  There is an excellent article on the net by the AZO Materials company, here is their link.

For those in a hurry or who are not too curious and want to read on, just briefly, what you need to know to continue:

Most metal-coated plastic components are made from ABS (Acrylonitrile Butadiene Styrene).  It is a versatile material, used in Lego blocks.  You know now?  It is a copolymer with three components.

  1. 15 – 35% — A –  Acrylonitrile — like vinyl, it’s tough and well wearing
  2.   5 – 30% — B –  Butadiene — the rubbery part, with self-polishing quality, adds elasticity
  3. 40 – 60% — S –  Styrene — brittle, known for dimensional stability and chemical resistance

Drawing 4 —  ABS

That’s what it looks like, drawing 4.  Different polymers don’t mix well, they form clusters, and they hinder each other from creating larger blocks.  They push each other apart.  Looking at it the opposite way, the plastics people’s way: styrene (green snakes) and nitrile (red barbed wires) crosslink the butadiene clusters (blue balls).  (Remember that for later.)

We used the product Terluran GP-35 for its high flowability during moulding, at the time manufactured by BASF.  I would have liked to tell you what its exact composition was, but after one hour of Internet search, I could not find any information on that.

I can tell you from memory, the vinyl component must have been near the high end, 30 – 35%, it was very difficult to break because of its high plastic deformation.  I also think that the styrene was near the upper end of 50 – 60%, because it machined well, with the right cutting angle. This leaves 15 – 20% for the butadiene component.  The presence of butadiene shows when the break area has whitish edges.

How is it done, roughly?

Photo 2 — Two types of ABS

First, the surface of the plastic component is etched in a heated solution, based on chromic acid (don’t touch it! and don’t even smell it).  In this process the butadiene component is removed from the surface of the component, selectively, providing a micro-etched finish to give bonding to the subsequently applied conductive layer.  Once that’s on, through vapour depositing, the electrolytic plating process continues like with any other metal.

Meeting the Expert

After a chat with the BASF ingeneers, their: “It should work!”, equipped with a bag of feeds and high hopes, I approached the electroplaters who had been recommended.

After a 4-hour drive, I arrived there.  First, they gave me a tour of the factory.  Smelly, hot, uncomfortable business.  I wondered how anyone could work in such an environment. Even though all wore protective clothing, face and breathing masks at some places, it seemed to me that no one would get away without any bodily harm.

After that, I met the technician.  With remarkably raised eyebrows, he first looked at the feeds on the table, long and fixated, and then at me, with a sad look and shaking head, at me.  “Can’t be done,” he explained.

For depositing, there needs to be an electric potential difference between the cathode (the depositing material) and the component surface; otherwise, there is no current flowing, and with no current, there is no transport nor depositing of metal. There would be no way of getting any metal into the capillaries or the slits.  My idea, depositing a metal coat onto the feed with had found its early end.

With a bit of thinking on my own, I could have worked it out myself but when one is excited, the mind respites, most of the time.  I wondered why the BASF people had given me the thumbs up?

It had been all over and done within two minutes.  Or, how long does it take to say the above?  Since it was lunchtime, and the technician knew that I had driven for hours to get here, he asked me out for a meal.  What is the topic of conversation one has with an electroplating expert?  The process of electroplating and its difficulties.  Electroplating of plastics had still been in its infancy, and he had considered me a plastics expert.

My question was: “How does one get the metallic vapour to adhere to the plastic?”  “It goes on after the edging and before the electrodeposition.”  He smiled, it must have been a good question.

He explained along these lines: “The acid solution nibbles away only the butadiene, the other components resist well.  One has to leave the plastic parts in the solution for some time.  The heating reduced its viscosity, and it can crawl into corners.  The acid chews into the surface, and since the butadiene molecule is much bigger than the other two components of ABS, cavities are created.”

ABS butatien take out cardboard

Drawing 5 — Cavities etched into ABS Surface

ABS electr plated

Drawing 6 — copper vapour deposited onto ABS

His sketch on the beer coaster looked similar to this, drawing 5.  The small cavities, as seen under an electron microscope at high magnification.  And then the vapour depositing happens.  At the time it was copper, now they use mostly nickel.  The copper anchors into the plastic surface like press studs, drawing 6.

He had several bits and pieces in his pocket. He showed me an etched component and one with deposited copper.  The etched part looked greyish like sandblasted. The copper-coated one looked just like solid copper, even with patina.

You know what came next.  The thought leading to the metal coating idea was to find a surface finish and treatment which would increase the feed’s acceptance of the ink. Now, an idea exploded: “Could these tiny cavities have the same effect as the 400 grit polishing cloth?”  It looked the same, greyish, perhaps, it works the same.  I told my technician about my problem.  Again his reply was not helpful: “The acid used is too viscous, therefore, it cannot enter into these small gaps.”  However, he could see my point.  Let’s give it a try and see what can be done by altering the acid’s viscosity.  I left him my bag of feeds.


Purpelish look on feed

Photo 2 — Purplish look on feed – source: internet

I was very excited and could hardly sleep.  Two days later, an express parcel arrived.   I dipped a feed in ink, and when I pulled it out, it was covered, saturated with ink, not evenly but everywhere. It had worked.  After drying in the oven, the feed had the purple sheen caused by the residue of ink pigment which had remained in the tiny cavities, it didn’t rub off, photo 2.

I knocked off early, ready for celebrating, organised the babysitter and took my wife out for dinner.  I told her what had happened.  I was so excited.  She thought I was nuts.


Next day I performed a complete feed test, with the feeds in the fountain pens.  What a disappointment.  The feed functioned only slightly better.  Much less than expected, indeed.  Oh, life’s a roller coaster.

Penetration into capillary

Drawing 7 — Cut along the ink capillary showing incomplete acid penetration into the capillary

I took an inked and etched feed (the grey part in drawing 7) and cut it apart, once along the ink capillary and once through the overflow capillary chamber.  It was evident, visible to my naked eyes.  The ink (purple colour) had barely and irregularly entered the capillaries, perhaps for half a millimetre and for about 1 – 1.5 mm into the overflow slits, they are wider.  The black section in the drawing marks the area where air had been trapped, thus, preventing the acid to penetrate into the capillary and the plastic is not edged, roughened.

The viscosity of the etching solution was too high to wick into the capillaries.  My helpful technician must have felt my despair.  Subsequently, we/he did some tests, trying to change the viscosity (heat and dilution) and agitating the bath.  No success in regards to what I wanted to achieve, however,  it improved the wettability of the plastic surfaces, which were not machined.  The machined surfaces did not need etching as urgently.

The manufacturing ingeneers ripped this progress “out of my hands” and included it in the production process.  Every bit helps.  I informed my technician, and I sensed his worries.  Now, he had to come up with an idea for passing those tiny pieces of plastic (my feeds) through his treatment process without disturbing the big jobs, such as chromed bumper bars and car trims.  Can you see my small feeds amongst them?

What had I learned?

  1. etching the surface gives enough roughness to promote surface action to a point where it behaves equivalent to rubber (we just can’t get the stuff into the capillaries)
  2. ABS seems the right material
  3. the process parameters of etching are easy to control
  4. etching is an affordable mass-production process and reduces production cost
  5. etched ABS could replace machined ABS as well as machined rubber

Rubbing it in / Initialising

While I had been exploring down the etching avenue, I also had been walking down another aisle.  One opened up when remembering being a boy at school writing with dip nibs.  Nibs rendered unsuitable for writing after one had played darts. We tried to bend the tines to their original position and then innocently told the teacher about our dilemma: “The nib doesn’t want to write anymore!”

Did he realise what was going on? He always gave us a new one. The pertinent point is that the new nib either didn’t hold the ink at all (it ran off) or pearled in droplets (like mercury).  It did not flow at all.  From the older boys, we had learned a trick.

We took a piece of cloth, or most often our fingers (parents didn’t like us using handkerchiefs, ink resisted washing out those days more than today and our fingers were permanently stained with ink, anyhow), dipped it/them in ink and – with quite some pressure – rubbed the nib between thumb and index finger from the rounded part to the tines and the tip.  After a few rubs, the nib took on the ink.  I didn’t know about the acid in the ink, but we could indeed perceive its particular odour which increased during rubbing.

How to transform this procedure (the rubbing) into a manufacturing process? Rubbing ink into the capillaries of a feed?  No, but injecting it with a miniature pressure jet mixed with fine sand?  Yes.  Afterwards, the feed could be washed and dried, and if needed the jetting could be repeated.  Washing would be ok because I wanted only that much ink to remain at the surface as it was absorbed by the microscopic cavities. Without any buildup, the mechanical dimensions of the capillaries would remain unchanged.

A messy business that had to be performed with each feed individually (not good for mass-production) however, I envisaged having an encapsulated robot to carry out this job.  Since this was a considerable investment and designing (my job!) this thing would take some time, I decided to try something else.

I built a tank from a 10-litre bucket (with a very tight lid), with several jets propelled by a fish tank pump and fins around the inside of the side walls.  Filled it with ink, it was the most turbulent ink whirlpool.  First I used a transparent lid because I wanted to observe the action but, as soon as the pumps started, all was blue. Long ago, I had learned to laugh about these little jerks. They happen all the time, a consequence of an excited, passionate mind.

Lamy_Safari-10-Feed no nib crop

Photo 3 — Initialising… after etching

Bathing the feeds in the whirlpool for several minutes helped the ink adhere to the feeds surface and the small impacts from the knocking at each other forced it to penetrate into the capillaries and fins, to some degree.  Adding a bit of acetic acid helped. By varying the ink injection pressure into the whirlpool, I could alter the degree of fluid agitation and increase the impact of the feeds against each other. In the early test trials, the feeds showed indents, which was prevented by reducing the injection pressure. This process increased the current feed’s performance even though they had not been etched.

As soon as I introduced this process to manufacturing, a bigger version was built and included in the production process.  We called it initialising.  Photo 3 shows a feed after initialising after it has been etched. You can appreciate that this process makes the surface more wettable… the contact angle reduces significantly.

The bath for production looked much like a top loader washing machine – our invention because all washing machines in Germany are frontloaders – while the dryer resembled a transfer oven set at low temperature. It had a  motor-driven belt made from steel mesh with the heat was created by infrared rods. It looked like a small pizza oven … what it looks like, today, in 2016.  Then, in 1979, pizzas were baked in wood-fired stone ovens with a steel plate.  We were just ahead of our time.

It’s interesting.  Once something works, one doesn’t talk much about it. No resting on the laurels; there weren’t any. The best was the appreciative looks of the manufacturing ingeneers who understood the improvement my work had presented. Life goes on.  The focus always remains on the unsolved challenges or problems.  Nevertheless, hardly ever did I feel pushed, it felt exciting, and I was on the hunt.

Remove Butadiene in other a Ways

As you know from my photo in the sidebar, I am an old hippie, and therefore, protection of the environment was/is an absolute must. With my high awareness of the impact our lives and actions bear on the environment, the idea of using strong acids in the manufacturing process of my product had me very concerned.  Hence, the train of thought occupied me: “Are there any other ways to remove the butadiene?”  Butadiene was the obvious target because it formed the largest clusters and it left beautiful cavities.  I looked for solvents, especially with lower viscosity so that it could penetrate deeper into the capillaries.  No luck.

Rough surface corner draw

Drawing 3 — Different scratches, different radii

While this was all going on, I had an opportunity to investigate the machined surface of a feed made of ABS through an electron microscope.  What a surprise.  I saw steep mountains and narrow ravines, nothing was as smooth as it appeared when seen with the bare eye, but rather like a giant had ripped the material away. It did not seem to be machined at all.  PS: Later I learned that all machined surfaces look like this, except electro-erosion.

Drawing 3 with the narrow angles from further up made real sense, now.  I show it here again so that you don’t need to scroll up and also so that I can show it off again. It’s pretty good, I reckon.

Removing Something else

“Why focus on the butadiene?” I don’t know when this thought crossed my mind the first time. The cavities do not need to be smooth.  I had learned that any old crack would do.  Knowing the fact about small angles, cracks appear to be even more efficient than smooth cavities.

The other components of ABS are, I repeat from above:

  1. ) 15 – 35% — Acrylonitrile
  2. ) 40 – 60% — Styrene

Because of its higher percentage, even higher than butadiene, styrene was my next target.  I knew already: Styrene is known for its chemical resistance and its companion, acrylonitrile, a vinyl, is pretty hardy against chemicals. Thus, it was to be expected that either would need something strong to decompose. You know me, I only would accept a process if it were less polluting than chromic acid, the butadiene eater. If I couldn’t find anything, I would never tell anyone about this solution. This is my responsibility as an ingeneer towards the world.

I talked with the chemists who suggested tri-ethylene glycol, abbreviated as TEG.  It is a standard product used in enormous quantities in gas and heating plants for cooling and maintenance, the removal of grease inside the machinery.  Before disposing, the TEG waste it is dissolved in water – which it does readily – but this only reduces its potency but not the actual amount (minus the evaporated quantity).  When used in small quantities, less than 100 liters, its disposal is often dubious. May this have been the case or not, I didn’t want to contribute to the use of this chemical, above all, it is hazardous to humans and the environment during the process.

Drawing 7 — Capillary filled

When I queried them about this fact, they suggested trying it in a test setup – which they had, and if it works principally, then there is polyethylene glycol, PEG, a safe but not as aggressive product used in the dry-cleaning process all over the world.  I only performed a few tests with TEG, using about 10ml and I knew, I was on a winner.

TEG caused the ABS to show the greyish, white surface I was looking for, and the capillaries absorbed the ink readily.  Cutting the feed along the capillary (drawing 7) showed that its low viscosity had allowed TEG to fully enter into the capillaries, all the way down.

What did I do with the TEG? After dissolving the 10 ml in 10 litres of water, I poured it in a very efficient manure heap (it stank), knowing confidently that those potent microbes would be able to handle this small amount.


I tried PEG.  The surface did not look as white as after the treatment with TEG.  After vigorous initialising, its capillarity improved, but not good enough for me to sign off.  There was no way for me to apply TEG, it was a no go.  Since no one was interested in my laboratory brewings, it was easy to hide this test result. I did not talk about this because I didn’t want anyone higher up to make a decision over my head.

From now on all my testing continued with PEG.  Warming up and agitating the bath helped, but the stuff evaporated quickly.  I put a lid on it, with a cooling coil attached to it.  The pump and controller from an old injection moulding tool did just fine.  Gee, it was all done on such a low budget.  Experience showed: As long as one doesn’t ask for money and one keeps the deadlines, they leave you alone.  Sometimes I wondered what they thought of me. Are/were they aware that I have been saving them thousands of dollars in production cost, just through the things that fell off my lab table while I was doing my “real” work?

Drawing 8 — trapped air-bubbles (the black parts, stylised)

The process using PEG improved, still, I was not happy.  After the initialising, I cut the feeds open and noticed the almost circular areas, which still had not been etched, drawing 8. Trapped air-bubbles! They prevented the solution of PEG from entering into the capillary. The more aggressive TEG could break the surface tension of the air-bubbles and therefore proceed, PEG could not.

How could I get rid of the trapped air-bubbles?


Whenever I found myself in a state like this, I liked to wander through the factory.  Watching the bustle in the manufacturing halls calmed my mind.  Mindfully I watched people work, engaged in conversations, often about their work which they knew in detail and very well.

They liked talking about it and possible improvements. For sure, there was a suggestion box but feeling, they could not express their ideas, the box remained empty, but they told me. I informed a well-meaning ingeneer responsible for the workplace, mentioning the person where the idea came from. In due course, the workplace was altered and the workers often received an award. For me, it was a distraction which helped my subconscience to sort itself out.

During my apprenticeship, I had mentioned my need for distraction to my old master. He knew that I was a bit odd, and he understood my behaviour.  His advice was: “Always have a bundle of drawings rolled up under your arm and look as if you had a target.

How is this all relevant?  During my aimless travels, I had learned that in the manufacturing of ball pen refills, an ultrasonic bath is used for cleaning the completed ball pen tips. They had to remove the lubricant for machining out of gaps of about 50 microns wide.  This process was entirely enclosed and automated, harsh chemicals were applied, TED I assumed.

This day, how opportune, I noticed on a shelf a small ultrasonic bath for testing, like for cleaning jewellery … something clicked … I borrowed it.  Fortune favours the sedulous.

Almost there

And here we are, almost at the end of this journey.  The bath had a heater, which I set to 60° Celsius, which I had found optimal before.  The frequencies ranged between 40 and 45 kHz depending on loading.

However, the results were not quite there, yet.  The etching treatment was inconsistent.  Some plastic pieces had been etched more than others… the greyness varied, noticeably.  On the positive side, the air-bubbles had reduced in size and number.


Acoustics had been my chosen speciality subject in the final years of my studies.  There we know, that in an enclosed space, when the air is under the influence of a particular sound frequency (under 200Hz, also depending on the dimensions of the space), then standing waves can form.

In this pattern, there are areas where sound energy accumulation and others where sound waves cancel each other out – to theoretically nothing – to practically only almost nothing.  Within this given space, the wave pattern remains in a stable position.  Therefore, when one moves through this space, one is subjected to varying levels of sound energy intensity.

This is what had occurred in the ultrasonic cleaner, standing wave pattern had caused the inconsistent etching.

At a hot chips shop, French fries in the US, “pommes frittes” in Europe (except the English, they always want to be different – Is that the reason why they call them Pommes?) I saw the guy frying the chips in a metal basket, and he moved it up and down.  Bingo!  The ingeneer never sleeps, never a dull moment.  The trigger for the next step.

In a kitchenware shop, I found a suitable (thin wire, open mesh) stainless steel strainer and went straight to work.  Half an hour later, a motorised rig moved the strainer gently up and down through the ultrasonic bath with a dozen of feeds in it.  It had to be a consistent number since any variation of material in the bath would dampen the wave energy to various degrees.  Minimising variables is just so crucial during research.

Drawing 7 — Capillary filled

The plastic surface took on the typical grey look, so I knew, it worked, only about ten minutes were enough.  I restrained my excitement and continued with performing the entire test.  The feeds were treated in my small initiation bath and dried. The capillarity test was excellent.  I cut several into pieces so I could see the inside of the capillaries.  Their surface was covered entirely with dried ink pigment, just like in drawing 7.

Why and how?  The tiny air-bubbles, which had been trapped in the capillaries were subjected to varying sound energy levels.  Through this, their surface skin was agitated, hence, they changed in size and burst.  Different bubble sizes need different energy levels; moving them through the pattern of varying sound energy provided this.  The next version of the test rig not only moved the basket up and down but also rotated it around its vertical axis.


The almost-final test had been carried out with standard production feeds inside the grip section, with a nib attached.  Production feeds at that time had machined ink capillaries and overflow chambers.  I performed all the tests I had developed to compare the function of fountain pens.  All went well.

The essential final question was still unanswered question: “Would the feed perform as well with injection moulded capillaries?”

Before committing to the high cost of a production mould, I carried out tests on samples produced in test moulds.  For simplicity of the mould, I had separate samples for ink capillaries and overflow chambers.  They completed with excellent results which were equivalent to feed capillaries machined in rubber.


I had proven what I had been out to prove, namely, that the quality of feeds made from an injection moulded ABS were equivalent to those from machined rubber.  As a matter of fact, the proven fact, they performed better.

The result was presented to the company manager, including all the top managers, and it was decided to take the risk (what risk?) and gradually move production over to injection moulded feeds. Except for a production size ultrasound bath, all other machinery for feed treatment had already been established in production.

Since this decision was outside the company manager’s knowledge, he looked very tortured, hence, how could I expect any praise?

Only after that time I was able to fine-tune the design for the new feed I had developed.  Before, the variation in test results due to inconsistency in the surface characteristics were too significant.  Possible small improvements, or tendencies thereof, had been swallowed by the variation of this parameter.

Old law for researchers: “Keep the number of variables small!”

Loose Ends

Now and then, I receive information from the readers of this site, which I read with interest and consideration and if appropriate, add it at the fitting place.

This way I found out that it took another 3 years before fountain pens in shops had the injection moulded feeds installed.  Apparently, this was in 1986.  Similarly, in 2019, I was informed by the mould designer of Parker that already in 1978 some fountain pen models worked with injection moulded feeds.  I am grateful that other oldtimers like me love sharing their knowledge.

Now, as I am writing about this study, in 2016, thirty years later, it appears nothing about the feed has changed.  Alas, after a recent (2018) bitter complaint of a reader, I would like to repeat that the feed appears to be the same.  Yes, the shape is still the same but without testing equipment, no one could tell if the feeds still undergo the process that I have described.  If not, the results would be inferior by a large degree.

Having said this with all due respect, allow me to proudly say:  If something has lasted this long and its quality is (mostly) undisputed, including the provision of evidence shown in the test results then the assumption is permissible that the conclusions drawn in this project were/are within the vicinity of being correct … even there may have been some magic involved.


The next chapter is about the concept of Development of the Feed and designing it.


Amadeus W.

26 July 2016

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7 thoughts on “2.9 Feeds Made of Plastic

  1. Damn this was cool to read. It makes me hyped about my degree (I still am debating mechatronics or computer science)

    I’m a maker and I really relate to the passion and all that xD

    I’m a bit confused tho, did they accept your design? It seemed like the last version was nice.

    You don’t know how modern ones are made right?

    I’ve found out a lot of nice pens (narwhal original with their jinhao shaped 6mm feed) and twbsi (which has a really cool air channel design)
    Seem to start wet and get drier after a page which I really hate! The only pens that are very consistent for me are lamy safari and pilot kakuno

    The lamy feed is really amazing tho, it seems that the wetness is very consistent and only determined by the tine gap

    I’ve always gotten a bit mad at the flaws of fountain pens so I wanted dto make a pen with a constant pressure on the ink chamber, and a feed/nib that opens the air channel with light pressure. Maybe a soap dispenser like mechanism that’d dispense ink with each touch

    Heck a digital pen that can control the flow via a peizo controlled air channel or even a diagram pump (this could even allow the pen to have two ink resirvors and switch between them during writing digitally giving the pen a sinewave color shifting pattern! That’d be SO COOL!

    Sadly I have no idea how much weight/space this would take. Depending on the power consumption it could be really light tbh
    Sadly I don’t have time or tools to try 😦

    At least the idea with the pressure activated air channel could work (more pressure would make the channel wider). Then this way you can let the ink drip down easily but only when nib is pushed down


  2. Thank you for sharing your experience in such deep detail with us fountain pen users.
    Please allow me the comparisons with cars: I do not need to understand the construction details of an diesel engine to be able driving a car. And so I do not need to understand all the construction details of a fountain pen t be able using it.
    Or wait! That’s only partly true! In both cases.
    As long as everything works as intended, no need to worry. It has always been and still is an advantage to know about the function of a tool in order to be able to help oneself in case of difficulty in unexpected situation.
    And the usual unexpected situations with fountain pens are: writing too dry, writing too wet, don’t write at all, having hard starts, inserting an ink cartridge in a new pen and nothing happens (oh, I laughed a lot about your pen testing machine!) or those nasty drops of inks falling from the tip of the pen before it touches the paper … 😉

    I learned a lot from your essay – with the most important part: keeping ingeneers busy in the hope to save money!


    • thanks, your comment made me smile… I would not be an ingeneer if that would be the most important part… 🙂 Except… there must be a few ingeneers who make things in the first place.


  3. Fascinating and very helpful. Thank you so much for taking the time to write all of it!! A labor of love in a time when every bit of information is monetized.
    I’m also looking to improve some home-made feeds, and pictures illustrating 1) the air hole and 2) the transition from the air channel to the overflow fins, would be helpful. I just can’t picture these in my mind.
    Again, thank you for all of this.


    • 1) The relationship between the air hole and the feed is only of importance when the air canal goes parallel or with the ink canal (on the top of the feed, as it is with feeds working with flex-nibs. Otherwise, the air hole isn’t really an air hole, and it can be anywhere where it is functionally required by the nib. Some nibs have no air hole.
      2) There is nothing special about the transition, the space of the overflow fins just opens into the air channel. Important is the difference in their widths. The width of the air channel should be significantly wider (twice as wide) so that the overflow fins don’t discharge into the air channel.

      Experiments give you more than too much thinking. If you want to publish your results on this site, I would consider it.
      enjoy, Amadeus


  4. I note with interest your comment that it was not until 1986 that fountain pen appeared with injection moulded feeds. I was a tool designer with Parker Pen Co. In my position I designed the injection moulded for their ‘Top line model ‘(1978) ‘Arrow model ‘ (1980) and the feed for their roller ball refills. All were injection moulded.


    • Thank you for your information. Do you know what material was used and if a particular surface treatment was applied? I would like to add your information to this page.


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