An alternative look at ink wetness

[LizEF]

15 minutes ago, squirrels said:

That's a very reasonable distinction to make. I suppose if there's no (or effectively no) ink evaporation it shouldn't matter how fast the ink dries on the nib for the purposes of hard starts.

That's exactly my thinking - ink drying is one thing, ink declining to come out of the nib and onto the paper is another.

[dipper]

14 minutes ago, LizEF said:

I also concede that I may be the only one with such a narrow definition of "hard start".  To me, "hard starts" is a consequence of baby's bottom. 

 

Experience in my 2020 project to improve the usability of "ruling pens" by altering the angles and profile shapes and metals used in the two pen blades revealed behaviours that may also occur with fountain pens.

 

I made lots of ruling pens in this project. Observation and diagnosis is easier with a ruling pen because the ink is fully exposed to view, and the gap at the tip of the tines is large enough to see exactly what the ink is doing under a 10× lens.

 

Here is what I saw:

 

Standard "baby bottom" occurred exactly as the fountain-pen textbook definition. Inner corners of the tines rounded too much --- ink sits slightly up, off the paper --- pen does not write --- unless pen is bumped down firmly onto the paper to jog the ink into contact, or if soft fuzzy paper is used with surface fibres that can touch the ink.

The term "hard start" seems appropriate.

 

With crisp inner corners on the two tines (no baby bottom) the shape of the ink meniscus between the tine tips is always concave, with varying degrees of curvature that depended on the overall design of the tines. However tightly concave that meniscus was though, if the meniscus edges were "attached" to the corners of the tines then whenever the tines touched paper the meniscus would instantly collapse down onto the paper and the pen would begin writing. "Easy start".

 

With some blade designs however the concave ink meniscus was not attached to the inner corners of the tines. It could be sitting about 1mm back from the tine tips. Some really bad blade designs were always like that. Some blade designs were OK when first dipped, but after about half the ink held from one dip had been used then the remaining ink would lift itself upwards to sit higher in the pen.

This occurred more with blade designs having narrower gaps higher up the blades, and especially with blades having a slim side-view profile and a sharp tip. (Rather like some fountain-pen nibs.)

In use, these ruling-pen-failures would write if bumped down onto the paper. If ink contact with paper can be made by bumping then the ink remains attached to the paper for the length of one pen stroke. But whenever the pen is lifted up off the paper then the ink hoists itself back up inside the pen again.

So the user experience was the same as with baby-bottom (Hard start), but the cause was different. I decided to name this design problem "ink tip drawback".

 

Moving from dipped ruling pens back to the subject of fountain pens it is conceivable that the pressure regulating process inside a fountain pen may go slightly awry and "pull" the ink up, away from the tine tips, as in my "ink tip drawback".

Conditions that might lead to such a state could include blockages in the air-breather paths - leading to too low a pressure inside the ink chamber after some period of writing, contamination on nib tines, or an unusually high surface tension ink.... but I am just guessing now.

 

For users experiencing "hard starts" here is one chink of light in the darkness (literally!) With a bright light behind the pen nib, and a 10× hand lens, in many fountain pen nibs the ink in the gap between the tines is visible, and an open gap with no ink is easily seen as light between the tines. (The ink meniscus at the nib tip is generally too small to study though.)

[LizEF]

1 hour ago, dipper said:

Experience in my 2020 project to improve the usability of "ruling pens"...

Fascinating!    Thank you for sharing this.  I had not considered the ink pulling back into the pen before.  And as far as I know, I haven't experienced it.  But now that I know, I can look for signs when others are describing problems, and have them check your list of potential causes, along with all the usual things we check.

[arcfide]

On 1/20/2022 at 12:07 AM, LizEF said:

I'm thinking maybe you should tip the bottle right side up again before opening the cap - especially if it's Baystate Blue...

 

LOL! Um, yeah, good idea....🤣

[arcfide]

22 hours ago, RJS said:

What is interesting to me is that a wet/low surface tension ink isn't always required to take what appears to be a dry writing pen (with fine nib) and make it feel like it's no longer a dry writer. Though a low surface tension ink in a fire hose of a pen does sound like a recipe for disaster.

 

Or it could be glorious!

[RJS]

8 hours ago, arcfide said:

 

Or it could be glorious!

Being glorious would require very special paper- ordinary high quality paper would be saturated and it would bleed and feather horribly. 

[RJS]

14 hours ago, LizEF said:

The speed at which ink dries out is definitely an attribute of the ink.  (But it's worth noting that if the pen seals well enough (Platinum 3776 Century or TWSBI Eco, for example), the ink ain't dryin' out in the capped pen.)

 

I don't consider "trying to write with a pen where the ink has dried on the nib / in the feed" to be "hard start".  Though others may well consider them the same thing.  And I concede, that it may seem the same to the user - especially one who hasn't experienced the difference.  I also concede that I may be the only one with such a narrow definition of "hard start".  To me, "hard starts" is a consequence of baby's bottom.  What you're describing is simply the ink drying.

I agree that hard starts are the consequence of baby's bottom, as skipping can be too. But why do only some inks behave badly in nibs with baby's bottom? Diamine Majestic Blue plays havoc with such pens, as an example.

[RJS]

13 hours ago, dipper said:

 

Experience in my 2020 project to improve the usability of "ruling pens" by altering the angles and profile shapes and metals used in the two pen blades revealed behaviours that may also occur with fountain pens.

 

I made lots of ruling pens in this project. Observation and diagnosis is easier with a ruling pen because the ink is fully exposed to view, and the gap at the tip of the tines is large enough to see exactly what the ink is doing under a 10× lens.

 

Here is what I saw:

 

Standard "baby bottom" occurred exactly as the fountain-pen textbook definition. Inner corners of the tines rounded too much --- ink sits slightly up, off the paper --- pen does not write --- unless pen is bumped down firmly onto the paper to jog the ink into contact, or if soft fuzzy paper is used with surface fibres that can touch the ink.

The term "hard start" seems appropriate.

 

With crisp inner corners on the two tines (no baby bottom) the shape of the ink meniscus between the tine tips is always concave, with varying degrees of curvature that depended on the overall design of the tines. However tightly concave that meniscus was though, if the meniscus edges were "attached" to the corners of the tines then whenever the tines touched paper the meniscus would instantly collapse down onto the paper and the pen would begin writing. "Easy start".

 

With some blade designs however the concave ink meniscus was not attached to the inner corners of the tines. It could be sitting about 1mm back from the tine tips. Some really bad blade designs were always like that. Some blade designs were OK when first dipped, but after about half the ink held from one dip had been used then the remaining ink would lift itself upwards to sit higher in the pen.

This occurred more with blade designs having narrower gaps higher up the blades, and especially with blades having a slim side-view profile and a sharp tip. (Rather like some fountain-pen nibs.)

In use, these ruling-pen-failures would write if bumped down onto the paper. If ink contact with paper can be made by bumping then the ink remains attached to the paper for the length of one pen stroke. But whenever the pen is lifted up off the paper then the ink hoists itself back up inside the pen again.

So the user experience was the same as with baby-bottom (Hard start), but the cause was different. I decided to name this design problem "ink tip drawback".

 

Moving from dipped ruling pens back to the subject of fountain pens it is conceivable that the pressure regulating process inside a fountain pen may go slightly awry and "pull" the ink up, away from the tine tips, as in my "ink tip drawback".

Conditions that might lead to such a state could include blockages in the air-breather paths - leading to too low a pressure inside the ink chamber after some period of writing, contamination on nib tines, or an unusually high surface tension ink.... but I am just guessing now.

 

For users experiencing "hard starts" here is one chink of light in the darkness (literally!) With a bright light behind the pen nib, and a 10× hand lens, in many fountain pen nibs the ink in the gap between the tines is visible, and an open gap with no ink is easily seen as light between the tines. (The ink meniscus at the nib tip is generally too small to study though.)

I'll second what Liz said- this was fascinating to read. Thank you.

[LizEF]

27 minutes ago, RJS said:

I agree that hard starts are the consequence of baby's bottom, as skipping can be too. But why do only some inks behave badly in nibs with baby's bottom? Diamine Majestic Blue plays havoc with such pens, as an example.

I know nothing about Diamine Majestic Blue, so it's difficult for me to guess.  But I will say that I think it's a mistake to draw general conclusions based on the behavior of an ink in a pen with a known flaw.  Baby's bottom isn't an alternate design, it's a flaw.  IMO, it should be fixed.  Therefore, I've never considered what ink to use in a pen with baby's bottom - I consider that question irrelevant - use whichever one you wish to lubricate the micromesh while you're fixing it.   (And yes, I recognize that some may disagree with my hard-nose approach.)

 

My instincts say that a wet-enough ink might overcome baby's bottom, as long as it's not too severe, but I'm not sure that's true.  The ink needs to be able to "suspend" low enough from the edges of the nib to touch paper, and I'm not sure which attributes would lead to that...  (Here is where my lack of science education shows - I sort of have to visualize and guess, but I can't use the various rules about how things behave to be sure of the attributes that lead to what I'm imagining. If that makes any sense.)

[InesF]

On 1/20/2022 at 4:08 PM, LizEF said:

... being able to write and write and write and write until the cows come home ...

... and until the chickens go to sleep ...

[InesF]

On 1/20/2022 at 6:33 PM, RJS said:

I forgot about a TWSBI pen I had filled with Monteverde Horizon Blue, one of my favourite inks. 3-4 months later it still wrote immediately, though clearly it contained less ink than it had. What was weird, when I wrote two pages with it, was how much wetter it wrote than usual- it spread more and soaked through the paper. Normally I expect the opposite, as inks seem to become thicker/drier/more lubricated as they evaporate. What has everyone else found in similar situations?

That's highly interesting!

As you write, me too would expect increased "well behaving" (=less spreading), but would expect a bit thinner (maybe not noticeable) and more intensely coloured line (concentrated ink) resulting in more ink delivery per line area.

Now I can only guess: maybe the detergent becomes more dominant and pulls the ink along the paper fibres...?  (I have no clue).🤫

[InesF]

On 1/21/2022 at 12:45 AM, dipper said:

Here is how I see it...

@dipper, thank you!

What a great read! Thank you for such a prosaic translation from my Denglish into English!

I can support every word you wrote there!

[InesF]

On 1/21/2022 at 4:12 AM, dipper said:

This occurred more with blade designs having narrower gaps higher up the blades, and especially with blades having a slim side-view profile and a sharp tip.

One more great observation! Thank you @dipper for sharing your experience with us!

 

Since some months now I try to figure out how to measure, scale and classify the properties of a pen (nib plus feed unit) according to pen writing wetness. By considering the physics behind, I'm sure about the dependency on the thinnest part of the whole ink flow channel compared to the thinnest part of the whole air flow channel. The difference between those two channels determines the pressure at which the ink is available at the tip of the nib - and consequently, how "ready" or how "willing" it is to flow.

Unfortunately I can't figure out a way to measure it. A ruling pen - exactly: a housed and sealed double ruling pen with one ink and one air channel may be the solution ....

 

Is somebody here in the forum who can build such a thing?

[InesF]

14 hours ago, LizEF said:

My instincts say that a wet-enough ink might overcome baby's bottom, as long as it's not too severe, but I'm not sure that's true. 

Indeed, @LizEF, so it is.

 

Low surface tension results in less concavity - or even zero, when the force downwards from gravity equals the capillary force at the tip.

 

But especially with B, BB and stub nibs, you're casting out the devil with a wet/low surface tension ink: you cure the babies bottom with a flood of ink with all consequences of feathering and bleed.

[LizEF]

8 hours ago, InesF said:

... and until the chickens go to sleep ...

"until (or when) the cows come home" is a fairly common American idiom meaning "a long, long time (if ever)".

 

7 hours ago, InesF said:

Indeed, @LizEF, so it is.

 

Low surface tension results in less concavity - or even zero, when the force downwards from gravity equals the capillary force at the tip.

 

But especially with B, BB and stub nibs, you're casting out the devil with a wet/low surface tension ink: you cure the babies bottom with a flood of ink with all consequences of feathering and bleed.

Thanks, Ines!

[dipper]

Is anybody ready for some more physics? ! !

 

Below is a theoretical model of baby-bottom. (Perhaps oversimplified as it is all shown in two dimensions, whilst nib-tips and ink interfaces are really three dimensional curved surfaces.)

 

 

Fig 1 is an enlarged view of two nib tines with an extreme case of baby bottom. Ink in the tines slit does not touch the paper, and the pen does not write.

The sketched magnifying glass indicates the area that is shown in Fig 2.

The ink meniscus is drawn in two example positions in Fig 2. Assuming the same ink is used, in both example positions the "Contact Angle" between ink and tines is the same. (The angle between the surface of the tines and the ink/air surface, measured through the ink.)

The ink meniscus will move up or down in the tines gap until the sum of all forces acting on it are zero. The ink meniscus will then be in "stable equilibrium".

 

The forces acting are best described as pressures. Here there are three:

Atmospheric Pressure acts into the ink (upwards as A in Fig 2).

Hydrostatic Pressure in the ink column acts outwards (downwards as P in Fig 2).

The combination of surface tension and the curvature of the meniscus creates another force, downwards in Fig 2 because the meniscus is concave. This is termed "Laplace Pressure", as L in Fig 2.

 

Let us assume the meniscus is actually in equilibrium in the lower of the two example positions. Then in that position,

A = ( P + L ),

or "upwards = downwards",

and the nett result is zero force.

 

But now consider what happens if the ink pressure P reduces slightly for some unspecified reason. The meniscus is then NOT in equilibrium. Pressure A is now winning the meniscus-pushing contest. Result..... the meniscus moves up the tines slit, away from the nib tip. How far will it move? Can it ever stop?

 

Yes, it can stop moving. Perhaps at the upper example position in Fig 2.

Pressure A continues to act strongly upwards. P continues to act downwards but is still rather whimpy and feeble. The "Laplace Pressure" L is the value that increases, and establishes a new equilibrium state. L increases because the curvature of the meniscus is greater in the upper position. (Check Fig 2, and note how the constant Contact Angle plays a part here.)

The increased value of L has compensated for the reduced value of P, and once again

A = ( P + L ).

 

If the pen's internal systems recover from whatever temporary problem caused P to reduce (trapped air bubble, now jogged free, say) then the process above will be reversed. The meniscus will move down towards the nib tip, and it will settle in a new lower-down equilibrium position.

 

That was fun.

 

Having seen the general theoretical principles of how an ink meniscus moves to find its equilibrium position, it would be great if we could now change to a different ink with, say, a higher surface tension, and figure-out the expected result. Unfortunately it's not that easy!

 

A higher surface tension will certainly give a greater Laplace Pressure L for some given meniscus curvature. The problem is the other values change also:

The pen's ink/air exchange and ink pressure control system relies on surface tension for its operation.... So the value of ink pressure P may change with the new ink.

The fixed Contact Angle used in sketching Fig 2 is a property of the ink/tine materials. If we change inks then that angle can have some different value.

 

One thing that remains certain is that the different ink will move in the pen nib until it finds its own equilibrium position, with some new combination of surface tension value, tines contact angle, surface curvatures, and ink hydrostatic pressure.

Will that position be higher up the tines slit? Or lower down? Or even touching the paper - so the pen actually writes now despite its excessive tip polishing?

That is anybody's guess! There are too many unknown variables to make a prediction.

 

 

[LizEF]

(initial reaction before reading beyond the diagrams) @dipper , I love the drawing / diagram.  It makes me smile.  That alone was worth coming to read.  (now I'll go read, professor)

 

21 minutes ago, dipper said:

That was fun.

Agreed!  (And has me wondering about unrelated claims regarding eyedropper pens burping more at high altitude, such as the Rocky Mountains, as opposed to low altitude, say Florida.  Or perhaps related to weather changes...)  Back to reading...

 

25 minutes ago, dipper said:

That is anybody's guess! There are too many unknown variables to make a prediction.

Clearly we need an ink & nib lab!  And scientists!  And lab techs, and study directors, and report writers, and ....... lots and lots of money!   (Or we could just use micromesh to get rid of the baby's bottom. )

 

Thank you for taking the time to draw and write that up for us.

[InesF]

6 hours ago, dipper said:

Is anybody ready for some more physics? ! !

6 hours ago, dipper said:

That was fun.

Always ready - so much fun!

Thank you @dipperfor this nice lecture and for the perfect drawings!

 

That's exactly what I had in mind - and what I have now an image to complement my imagination.

With your explanation you initiated another thought: The equilibrium, as you explain it, will be the result of surface tension of the ink, surface wetability of tines and tipping, capillary forces along the ink channel and current ink-reservoir-air-bubble-pressure difference to ambient air pressure - and maybe a bit of gravity driven mass inertia resulting from pen movement (a quick movement downwards with a rapid deceleration may initiate a line drawing of a pen suffering from babies bottom).

 

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?

[InesF]

6 hours ago, LizEF said:

Clearly we need an ink & nib lab!  And scientists!  And lab techs, and study directors, and report writers, and ....... lots and lots of money!   (Or we could just use micromesh to get rid of the baby's bottom. )

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 ... 😇)

[InesF]

21 minutes ago, InesF said:

current ink-reservoir-air-bubble-pressure difference to ambient air pressure

Hmm, or not?

Until equilibrium is reached, any surplus ink flowing down towards nib will be sucked up in the feed reservoir. Finally the ink pressure will be the same (=constant)?