An alternative look at ink wetness

[LizEF]

  On 1/25/2022 at 9:59 AM, InesF said:

Hi @LizEF - a virtual lab is a lab!

I think, based on the discussion here we have already built a hybrid between round table and ink laboratory.

 

Next step is a workshop session at one of the fountain pen shows ...

(... I have a déjà vu ... 😇)

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[dipper]

  On 1/25/2022 at 9:52 AM, InesF said:

In the writing equilibrium there is the counter-force of the upwards rising air bubble in the breather channel which also counters some of the other forces, as mentioned above and still in place.

Looking forward to your opinion: can that be calculated based on capillary diameters?

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Some things can be calculated easily. (Including static capillary pressure in a narrow parallel-sided ink channel. Equation for that at the end of this post.)

 

Some things are just way too complicated for any reliable mathematical modelling. We may be able to make-do with theoretical approximations and simplifications. Or it may be better to work by practical experiments, prototype designs and testing.

 

In fountain pens, anything to do with FLOW is likely to be super complicated. Generally with solid objects "dynamics" is more difficult than "statics". If liquid moving ink is introduced into the picture we are entering the field of fluid dynamics. "Not easy" is an understatement.

 

In the baby-bottom analysis that I posted yesterday there was no flow. The ink was sitting stationary in the nib slit. So we can draw a diagram, apply some known laws of physics, and reach some useful conclusions. (Despite some simplifications and omissions.)

 

Also things get complicated when various parts interact as a system. And a fountain pen is a system of parts. Even if we understand each part individually, the behaviours of the total system can be complex. Some simple systems of a few simple parts turn out to exhibit chaotic behaviours. For example this pendulum:

 

 

For discussions of the overall system of a fountain pen, we really need diagrams of any features that are also being described in words. ( E.g. "feed reservoir"? I don't know what that is.)

 

- - - - ------ - - - ------ - - - -----

 

How much "suck" does a capillary slot have? (From old notebooks)..

Top left is the system diagram: A chamber with ink and some air, at pressure P. Some sort of pipe connection from ink to the outside world.... where the atmospheric pressure is A.

 

P is less than A. So A could push the ink back into the sealed chamber? Or the ink could move out, into the pipe/slot/channel, if capillary action is enough to overcome the pressure difference (A-P).

 

The calculations case 1, 2, 3 etc are for different shapes of connection pipe. For a flat walled capillary slot, as seen in most fountain pen feeds, see case 2 on right hand page.

Capillary action will draw ink out, into the slot, if 2 × surface tension × cosine of (contact angle between ink and feed material) ÷ width of the slot IS GREATER THAN the pressure difference between Atmospheric pressure and the pressure inside the sealed chamber.

 

In later pages (not photographed) I calculated with these example values:

S.Tension = 47 mN/m

Contact Angle = 50 deg

Slot width d = 0.1mm

 

Result: Capillary "draw pressure effect" = 604 Pa

That is about 0.6% of standard atmospheric pressure.

 

So, if the pen's breather/ink/air system can maintain the pressure in the ink chamber at about 0.3% below external pressure (at 99.7% × A). Then despite the nett pressure (A-P) acting into the ink chamber, the ink will still move out to fill the capillary slot.

Ahah... the theory seems to work!

 

 

 

[LizEF]

Liz's brain before this thread: 🧠

 

Liz's brain after this thread: 🧠

 

[InesF]

  On 1/26/2022 at 1:40 AM, dipper said:

S.Tension = 47 mN/m

Contact Angle = 50 deg

Slot width d = 0.1mm

 

Result: Capillary "draw pressure effect" = 604 Pa

That is about 0.6% of standard atmospheric pressure.

 

So, if the pen's breather/ink/air system can maintain the pressure in the ink chamber at about 0.3% below external pressure (at 99.7% × A). Then despite the nett pressure (A-P) acting into the ink chamber, the ink will still move out to fill the capillary slot.

Ahah... the theory seems to work!

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Thank you, @dipper for sharing your experience with us! It's a pleasure!

 

I try to recapitulate and express with my range of words:

When steady writing (or drawing lines) reaches the point where the air bubble pressure in the ink chamber counters the capillary pressure in the ink channel (capP - chambP = 0) the ink will stop flowing (capillary suction of the space between paper fibres left aside). To never ever reach this point, a second channel (separately or combined via a breather hole) with larger inner diameter and lower static capillary pressure is necessary.

In the writing/drawing situation with steady ink flow and with a two-capillary dynamic steady state pressure difference the amount of ink delivered (again, letting the paper influence aside) will depend on surface tension of the ink and capillary diameter difference. At a given writing situation (one pen, one ink, one paper), both are constant.

 

I'm totally with you: empiric testing and design adaptation may be the way to go.

Nevertheless, I can draw an imaginary picture for myself.

Thank you!

 

btw.: with feed reservoir I meant the amount of ink that can be sucked and kept in the overflow slits of the feed.

Edit (forgot at first): all these ideas are heavily inspired by Amadeus W's ingeneer page!

 

  On 1/26/2022 at 1:55 AM, LizEF said:

Liz's brain before this thread: 🧠

 

Liz's brain after this thread: 🧠

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@LizEF, please allow me to join! 😊

+1

Edited January 26, 2022 by InesF
Link added

[LizEF]

  On 1/26/2022 at 8:33 AM, InesF said:

@LizEF, please allow me to join! 😊

+1

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[dipper]

There is only one capillary path. It goes from the ink chamber, down through the feed, into the nib slit, and out onto the paper.

 

There is also an air path that allows air to enter the ink chamber. That is not a "capillary" slot, it is a wide-open channel full of air.

 

Pressure in the ink chamber is regulated to a value slightly below atmospheric pressure by the effect of surface tension in the curved interface between air and ink at the point where the tip of the air path pokes up into the ink chamber.

In this sketch of a cross-section of a Sailor fountain pen feed the air enters underneath the feed, goes up into the section, passes around both sides of the feed, meets the ink capillary slot somewhere beneath the shank of the nib, and then passes upwards (on top of the ink slot) up into the ink chamber.

The  small 3D sketch shows the tip of the feed poking up through the back end of the pen section into the ink chamber. Both the ink capillary slot opening and the air breather channel opening are emphasised. In the actual Sailor pen the outer plastic ring is taller than I have sketched, and sharply pointed to pierce the ink cartridge or to fit snug into a converter.

 

 

[RJS]

I'm constantly impressed by the posts contributed to this thread!

[LizEF]

  On 1/27/2022 at 12:45 AM, dipper said:

In this sketch of a cross-section of a Sailor fountain pen feed the air enters underneath the feed, goes up into the section, passes around both sides of the feed, meets the ink capillary slot somewhere beneath the shank of the nib, and then passes upwards (on top of the ink slot) up into the ink chamber.

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Thank you for another interesting post!

 

(Background: I have never researched or examined a feed in detail, so I'm coming from a place of mostly ignorance beyond the basics any user might now.)

 

Now I'm curious, so, a few questions:

1. The bold bits read to me like the ink and air share a channel (at least once they meet).  Except, "on top of the ink slot" might mean there's a separate channel, and the drawing has them separate (though that could just be for convenience), I'm not certain.  So, do they share a channel, or have separate channels?
2. If they share a channel, does that simply mean that these forces we're talking about are what allow them to co-exist (as it were)?  They're so perfectly balanced that ink and air stay put until something (shaking, writing, your airplane taking off) disturbs the balance, and then everything starts moving until we balance out again?  (My brain is trying to figure out why it's not all air or all ink - one shoving the other out, so to speak.)
3. Also, if they share a channel, I'm guessing the ink and air aren't quite so separate as your drawing shows them?  That is, I would expect some air bubbles in the ink in that channel - yeah, air would rise to the top, being lighter, but I'm guessing the interface isn't quite so perfectly divided?
4. If I'm wrong, and they have separate channels, I'll have more questions.

 

Mostly unrelated note: this thread has sparked my curiosity, and so I dug out my real microscope (it's this thing, which I bought way back in 2005), and I've been working with tech support to get its camera working with Windows 7 or 10 so I can capture images from it.  We've reached the point where I can't go forward without a 32-bit version of Windows. Someone shoot me for not upgrading the camera firmware 10 years ago...   If I can find such a computer, then I'll be able to take pictures of what I see.  I now plan to stick a transparent feed under it and see if I can see anything interesting (magnification may be too great, but I can try).  And, I plan to examine ink and writing with it, to see if that's interesting.

[arcfide]

  On 1/27/2022 at 2:20 AM, LizEF said:

I can't go forward without a 32-bit version of Windows.

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If you haven't done this already, it's possible to set up a "Virtual Machine" using VirtualBox, VMWare, or other software to run a 32-bit version of Windows inside of a virtual computer, which might let you do what you want to do. 

[arcfide]

  On 1/27/2022 at 12:45 AM, dipper said:

There is only one capillary path.

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When you talk about there being only one capillary path, do you mean that the multiple channels and cuts and grooves inside of some feeds should be considered a single capillary path, or that most feeds you've examined have only one single ink channel? 

[InesF]

  On 1/27/2022 at 12:45 AM, dipper said:

In this sketch of a cross-section of a Sailor fountain pen feed

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Great, simply great! I love your drawings!

(I now try to bait more of those drawings out ... 😉)

 

Indeed, the air channel must be much bigger in diameter than the ink channel and even the ink channel changes its diameter at least once, likely several times along its path.

Looking at the inkward ends of my Waterman feeds, I see three slits in different sizes, Pelikan has two, Aurora has 2 ½ (I'm not sure if one of them is only a groove or a real channel) and Santini has only one.

And agin, I like to point towards Amadeus W's homepage where he also speaks about two channels as the "normal" variant.

 

My Waterman feeds of Carene, Serenite and Perspective behave absurdly special during cleaning: I can force water through the nib-feed-section-unit until it runs out colourless, can than shake it and use paper towel to suck it dry, whatever - all clean. But the moment I blow air through, almost undiluted ink, which was hiding somewhere in the feed, runs out. I can (and must) repeat this until the feed is out of ink in this hidden "something"-reservoir. Carene and Serentite have a 90° sidewards oriented breather hole and after all water ran out, a short blow with air causes a sideways fountain (reminder: its called "fountain" pen). 😄

 

  On 1/27/2022 at 2:20 AM, LizEF said:

If they share a channel, does that simply mean that these forces we're talking about are what allow them to co-exist (as it were)?

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To my understanding: yes, if there is only one channel.

Nice engineer (or ingeneer) construction work, isn't it?

 

 

PS: at weekend I will do macro photos of these feeds.

[InesF]

  On 1/27/2022 at 1:17 AM, RJS said:

I'm constantly impressed by the posts contributed to this thread!

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Me too! +1 👍

[LizEF]

  On 1/27/2022 at 5:02 AM, arcfide said:

If you haven't done this already, it's possible to set up a "Virtual Machine" using VirtualBox, VMWare, or other software to run a 32-bit version of Windows inside of a virtual computer, which might let you do what you want to do. 

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That was my first thought, since my Windows 7 (64-bit) has XP Mode installed, but apparently that won't work (confirmed with the tech support guy, and don't want to take risks - screw up the firmware update and the camera is hosed permanently).  But thank you for the suggestion.

[LizEF]

  On 1/27/2022 at 9:54 AM, InesF said:

(I now try to bait more of those drawings out ... 😉)

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👏

 

  On 1/27/2022 at 9:54 AM, InesF said:

I can force water through the nib-feed-section-unit until it runs out colourless, can than shake it and use paper towel to suck it dry, whatever - all clean. But the moment I blow air through, almost undiluted ink, which was hiding somewhere in the feed, runs out. I can (and must) repeat this until the feed is out of ink in this hidden "something"-reservoir. Carene and Serentite have a 90° sidewards oriented breather hole and after all water ran out, a short blow with air causes a sideways fountain (reminder: its called "fountain" pen). 😄

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  Anybody know where we can get a borescope with a diameter measured in fractions of a millimeter?  Or a nanite, maybe?

 

  On 1/27/2022 at 9:54 AM, InesF said:

To my understanding: yes, if there is only one channel.

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Thank you.  Your post brings up my "separate channels" question, though: what keeps them (ink and air) out of each other's channels?

 

  On 1/27/2022 at 9:54 AM, InesF said:

Nice engineer (or ingeneer) construction work, isn't it?

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Interestingly, science is supposed to give us understanding of how things work, but the more we discuss all this, the more it seems like fountain pens are magic! It's a wonder they work at all (instead of holding on to all the ink, or running it out in a flood).  Somebody somewhere somewhen was a genius!

 

  On 1/27/2022 at 9:54 AM, InesF said:

PS: at weekend I will do macro photos of these feeds.

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Oh goody!  Should be exciting.

[RJS]

  On 1/27/2022 at 2:32 PM, LizEF said:

Interestingly, science is supposed to give us understanding of how things work, but the more we discuss all this, the more it seems like fountain pens are magic! It's a wonder they work at all (instead of holding on to all the ink, or running it out in a flood).  Somebody somewhere somewhen was a genius!

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It does begin to feel like magic, doesn't it! It must be a nightmare designing high quality inks and pens, if this is anything to go by. 😅

[LizEF]

  On 1/27/2022 at 2:39 PM, RJS said:

It does begin to feel like magic, doesn't it! It must be a nightmare designing high quality inks and pens, if this is anything to go by. 😅

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I think it's one of those situations where you have to say, "We're not sure why it works, but it works, so we're going with it!"

[RJS]

  On 1/27/2022 at 3:09 PM, LizEF said:

I think it's one of those situations where you have to say, "We're not sure why it works, but it works, so we're going with it!"

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Exactly! God only knows what they put in my trusty Pilot Blue Black, considering the unpleasant smell, but the darn stuff behaves so well and develops excellent water resistance- if I was another company I'd try to isolate some of the weird ingredients that ink must contain, and throw it in my own formulation to see if it helps!

[LizEF]

  On 1/27/2022 at 5:43 PM, RJS said:

if I was another company I'd try to isolate some of the weird ingredients that ink must contain

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That's actually not so hard - a relatively simple chemical test.  When I worked (in IT) at a lab, one of the chemists had memorized the look of the graph-like report of chemicals that make up Coca-Cola, because people sent it in so often to have it analyzed, as if it were something of their own make (presumably so they could do exactly what you describe).  I think it was the TOC machine that put out this report, but it was a long time ago and I could be wrong.  Anyway, they'd run the test, not knowing what the sample was, and as soon as he saw the report, he'd say, "Someone sent us Coke again."

[RJS]

  On 1/27/2022 at 6:07 PM, LizEF said:

That's actually not so hard - a relatively simple chemical test.  When I worked (in IT) at a lab, one of the chemists had memorized the look of the graph-like report of chemicals that make up Coca-Cola, because people sent it in so often to have it analyzed, as if it were something of their own make (presumably so they could do exactly what you describe).  I think it was the TOC machine that put out this report, but it was a long time ago and I could be wrong.  Anyway, they'd run the test, not knowing what the sample was, and as soon as he saw the report, he'd say, "Someone sent us Coke again."

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I assumed that was the easy bit- understanding why they do what they do in combination with each other is the trickier bit! Hence some experimenting with whatever mystery ingredients they have in there that do the magic... But even Pilot don't seem to replicate the water resistance that their BB has in their other inks  🤷🏼‍♂️ 

[LizEF]

  On 1/27/2022 at 9:07 PM, RJS said:

I assumed that was the easy bit- understanding why they do what they do in combination with each other is the trickier bit! Hence some experimenting with whatever mystery ingredients they have in there that do the magic... But even Pilot don't seem to replicate the water resistance that their BB has in their other inks  🤷🏼‍♂️ 

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The water resistance is probably a side-effect of everything else (or a natural attribute of the dye + other ingredients) so that they can't replicate it without also changing the color (of the other ink).