An alternative look at ink wetness

[LizEF]

@InesF, I hope you don't mind, but I thought your thread would be a good place to ask this question, hoping to get some input from the highly educated scientists on our forum!  I'm wondering what sort of pen (if any) would work best for a human to judge ink flow by writing and observing.

 

By way of example: the Japanese EF is, IMO, the perfect tool for measuring lubrication.  It would be very difficult to measure lubrication with a super-smooth big broad nib - every ink, even the poorly lubricated, would feel smooth.  With a Japanese EF, however, the ink makes a significant difference in how the nib feels.

 

But is there a similar beast for flow?  Would a dry pen be right, because it would reveal the ink's behavior?  Or would you want a wet pen, to see if the ink can keep up with demand?  Either way, I'm thinking you'd want a broader nib - again, so there's more demand on the ink.  But I can't seem to decide which, if any pen attributes would best reveal ink wetness.  Perhaps it's something that requires scientific instruments and measurements...

 

One thing I'm pretty sure of is that my EF review pen isn't the right tool for the job.  It's fine for saying how ink flows in an EF, but not for predicting flow from other pens, I think.  I'm also wondering if there's more going on here - since there's an ink in my review pen right now that I consider very dry, but the person who gifted it to me considers it wet - I don't think we're both right!  Maybe it's clogging my EF pen, but doesn't clog larger-nib pens, and thus my perception of flow is thrown off by clogging?  I'm currently under the assumption that the quick drying on the nib and today's clog-that-required-dipping-in-water mean it's dry...

 

Can anyone help out this poor uneducated scribbler?

[InesF]

Hi @LizEF, you are welcome!

Indeed, that's a good question.

 

The more general recommendation would be: use a stiff, round, (western) medium nib, steel or gold doesn't matter. The nib + feed should be a medium or dry writer. Do not dip, fill a cartridge or converter, make sure the feed is wet but not flooded when you start the test.

 

The background is in the reproducibility of the setup. A stiff round nib (with round I mean no line variation) should always draw similar lines and you may already get a quick first impression from the line width. All fine and extra fine nibs I have tested so far were not or only minor susceptible to smaller surface tension variations - the can work well with low surface tension inks and you would not recognise the wetness. Neither half-soaked nor flooded feed is obvious, but not dipping is the advice to avoid the unpredictable degree of filling.

 

A medium nib will not be less prone to clogging than a EF. The nib slit is the limiting factor (but more often the particles will be caught already in the feed) and can and should be very similar for the nibs, at least independent from the tipping size.

 

Hope that gives a good orientation.

I prefer to use one of my stiff Waterman pens for some testing - and I do the measurements to get an idea about the behaviour and about possible problems.

[LizEF]

  On 2/6/2023 at 8:42 AM, InesF said:

All fine and extra fine nibs I have tested so far were not or only minor susceptible to smaller surface tension variations - the can work well with low surface tension inks and you would not recognise the wetness.

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Yes, this is the conclusion I came to some time ago - hence the question.

 

  On 2/6/2023 at 8:42 AM, InesF said:

The more general recommendation would be: use a stiff, round, (western) medium nib, steel or gold doesn't matter. The nib + feed should be a medium or dry writer. Do not dip, fill a cartridge or converter, make sure the feed is wet but not flooded when you start the test.

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Thank you!  This makes sense, even if it's only my instincts that understand.   Interestingly, I don't have a single medium nib.   (Well, I have a Jinhao nib that I think is a medium, based on line width, but it doesn't have markings.)  I'll have to ponder whether I want to get a nib (unit) or pen for this.  Right now, I just wanted to solidify in my head what I would need to test this (short of building a machine - for which my brother helped me pick out some parts, but I don't think I want to go there).  Unfortunately, An Ink Guy hasn't tested every ink!   And that leaves me "guessing" at wetness for some of the inks I test.  (See point #1 - EF nibs...)  While I ponder, I'll be satisfied with informing my viewers that the ink flows fine in my EF nib - or not, on rare occasion.

 

Thanks again for your help on this, and this great thread!

[InesF]

  On 2/6/2023 at 1:17 PM, LizEF said:

Interestingly, I don't have a single medium nib.

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Doesn't matter, as long as it draws a line in the range of 0.5 to 0.7 mm - and, you should always use the same nib, feed and paper for comparative tests.

(yes, hold some paper on stock for the testing)

 

Good luck!

And thank you for your always appreciated comments! 😊

[LizEF]

  On 2/6/2023 at 2:04 PM, InesF said:

Doesn't matter, as long as it draws a line in the range of 0.5 to 0.7 mm - and, you should always use the same nib, feed and paper for comparative tests.

(yes, hold some paper on stock for the testing)

 

Good luck!

And thank you for your always appreciated comments! 😊

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Thank you!

 

And you're most welcome!

[InesF]

Another short update of the ink list. The collection grew as I broke my moratorium. Now we count 99 inks; I would prefer not to let the number grow to three digits ...

 

I also re-structured the center part. Still not optimal, but maybe a better way to describe the uncertainties in this middle range of surface tensions.

 

PS: I love the new-to-me Taccia inks - great performers! Bleu Austral is more tamed than the low surface tension may suggest, as it is originally of high viscosity.

[InesF]

Before going into the summer break, here a quick update of ink properties, now counting 111 inks and the list is still growing!  

 

[ferrogallic]

I found an interesting patent that claims wetness mainly correlates with the wetting angle on the nib. They reduce wetness by adding a flotation agent to increase the wetting angle, while still lowering the surface tension of the ink itself. I have summed up the patent in a different thread:

 

[txomsy]

  On 10/26/2023 at 5:43 AM, ferrogallic said:

I found an interesting patent that claims wetness mainly correlates with the wetting angle on the nib. They reduce wetness by adding a flotation agent to increase the wetting angle, while still lowering the surface tension of the ink itself. I have summed up the patent in a different thread:

 

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Maybe I am missing something here.

 

Doesn't the wetting angle depend on the surface tension, which in turn depends on the gas, liquid and solid properties and temperature?

 

We can assume the gas to always be air and of little variation, temperature similarly, more or less the same in almost all cases (room temperature). Since the solids cannot be accounted for when designing a generic ink (different nib alloys, feed materials and a huge variety of papers), one must accept different behaviors in different pens and papers or optimize for only some specific combination.

 

Surface tension (fluid-gas) will come into play when there is gas: i.e. in the converter/cartridge/ink reservoir of the pen, and once it reaches the tip of the nib.

 

If we want a generic ink, it must work on any combination of ink-channel/nib/paper material.

 

If we want an ink optimized for a pen model, we can optimize the fluid/pen-solids interfaces.

 

If we want an ink optimized for some paper, we can work on both the fluid/solid (paper) and fluid/gas (air) interfaces.

 

If we want to control blobs and spills, we need to work at the feed/channel and at the tip, i.e. both, the fluid/solid and fluid/gas interfaces. In the patent they say that generic inks have (or find convenient to use, or are forced to choose, or have found as the best choice) similar fluid/gas (surface tension) properties, so they decide to work on the fluid/solid interface.

 

But surface tension (fluid/gas) does also matter, both at the nib tip and the paper surface. Ink drying, for instance, will depend on both the ink/metal and the ink/air surfaces.

 

In all cases, you are playing with different surfactants that affect either ink-pen surfaces or ink-paper surfaces or ink-air surfaces.

 

Their claim is that you can either aim for a general solution (by choosing an ink composition that works more or less well in all conditions) or you can specialize in one kind of surfaces to improve behavior on those, sacrificing generalization; and then they look at how to optimize the ink for gold nibs, to reduce leaks/blobs with the pen nib-down, and then they try to reduce feathering by adding a compound that will affect little stickability to metals but will stick to paper (starch).

 

Bentonite may act like balls in cartridges and converters, by including porous/fibrous clay micro-particles that probably reduce ink cohesiveness, improving flow, and that might help fix and deliver ink (like micro-sponges) to porous, fibrous paper.

 

To me, that means they are designing a specialist ink good for gold nibs, in pens resistant to alkali (remember that the so much maligned BSB is also an alkaline ink), with wide ink channels (they do not consider ink-ink channel/feed interactions), to be used on non-coated paper.

 

In other words, in the multi-dimensional space of nib-surface, ink channel, feed surface, pen materials and paper surfaces, they choose a direction (a combination) and optimize for it. Their ink will work well under those assumptions and might fall short compared to others under different conditions.

 

That is probably why many pen manufacturers would "optimize" their inks for their pen materials and advice you to preferably use their inks on their pens.

[ferrogallic]

You are not missing anything, I think the trick is that they very selectively change the surface energy of the ink-metal interface, while leaving the ink-air and the in-paper interface as is.

If we added a surfactant, it would affect all of them.

 

The angle is given by Young's equation

 

 

These flotations agents are used for separating ore from rock, I don't know how their mechanism, but clearly they must be very surface selective. It makes sense that it mainly attaches to the metal and not to the paper.

 

At the concentrations mentioned in the patent (0.02%, mmol/l), the change in surface tension would be very small, roughly similar to the graph in the Han paper:

Yet, this small change would still lead to a contact angle change from 0 to 30 deg.

 

The paper by Witt has a much better plot in Fig. 2 for a couple more different compounds, including the one referenced in the patent. I didn't manage to paste it here.

 

The effect also depends on the pH, according to this document, p24, the contact angle goes up with lower pH.

 

 

  Quote

 

Bentonite may act like balls in cartridges and converters, by including porous/fibrous clay micro-particles that probably reduce ink cohesiveness, improving flow, and that might help fix and deliver ink (like micro-sponges) to porous, fibrous paper.

 

 

 

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That is an interesting thought! Amadeus W writes that he developed a surface treatment to make the surface rougher, maybe the clay deposits on the surface of the feed and does the same.

https://fountainpendesign.wordpress.com/fountain-pen-feed-function/feed-plastic-injection-moulded-acid-treatment/

 

 

 

 

This is not my field at all, maybe we have someone from the mining industry who can explain more.

 

It would be a very interesting experiment to add a small amount to inks and see whether it reduces the wetness.

[txomsy]

  On 10/26/2023 at 5:33 PM, ferrogallic said:

The effect also depends on the pH, according to this document, p24, the contact angle goes up with lower pH.

 

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What defines the behavior of the fluid is the interaction of its molecules with the surface. Changing pH may change molecular charges available for interactions, thus affecting the interaction.

 

E.g. some H+ ions might combine with negative charges quenching them, or sequester loose-bound atoms, or induce charges in ionizable groups/molecules/surfaces.

 

Thus, depending on materials, charge distributions may change more or less with pH. This will affect the behavior of solutions like inks, possibly in complex, time-dependent ways.

For instance, air O2 infused in a solution may oxidize H+ to produce H2O and increase pH (and oxidize other components of the writing system too).

 

Pen, paper or ink nanoparticle surfaces may experience charge changes as well. Fe2O3 nanoparticles have been found to switch charge (- to +) with a pH change of 8 to 10.

 

Metals tend to lose electrons (so get positively charged surfaces), plastics tend to get negative charges.

 

It will be these charges that will define the cohesiveness and behavior of fluids on surfaces.

 

Plus, charged surfaces may attract oppositely charged ink components (forming films or clogging) also changing their behavior.

 

So it gets complex very fast. But at the bottom, although the effect of pH on water should be negligible (from pH 1 to 13), its effect on other components of the writing system may be noticeable depending on the properties of the pen, paper and ink materials.

 

Added: but note also that the pH scale is logarithmic, and IMHO probably its significance is strongly dependent on the materials and material combinations involved, and probably small in most FP-related contexts (with a special exception for long-periods air-exposed IG inks). But do not take my word from it. This is mostly speculation on my side.

[InesF]

  On 10/26/2023 at 5:43 AM, ferrogallic said:

[...] that claims wetness mainly correlates with the wetting angle on the nib

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  On 10/26/2023 at 7:38 AM, txomsy said:

Doesn't the wetting angle depend on the surface tension, which in turn depends on the gas, liquid and solid properties and temperature?

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Exactly that! 

 

  On 10/26/2023 at 5:33 PM, ferrogallic said:

At the concentrations mentioned in the patent (0.02%, mmol/l), [...]

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Here the patent is, as so many others are, vague! 0.02% is MUCH different from 40 mmol/l. Derivatisation of xanthan may break some bondings in the polymer chain. The molecular weight may still be high and 20 or 40 mmol/l may be an almost solidified mixture. Xanthan is thixotropic, that means its viscosity is reduced during stirring (or during flow). ... ➝ 

  On 10/27/2023 at 10:09 AM, txomsy said:

So it gets complex very fast. [...]

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!!

 

  On 10/27/2023 at 10:09 AM, txomsy said:

Added: but note also that the pH scale is logarithmic, and IMHO probably its significance is strongly dependent on the materials and material combinations involved, and probably small in most FP-related contexts [...]

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Yes, @txomsy, your word can be taken!

 

PS @ferrogallic: I gave a longer answer in the other thread.

[ferrogallic]

Very interesting! I always thought that pH changed the surface tension, but you are right, the surface tension is nearly completely constant with pH:

https://www.sciencedirect.com/science/article/abs/pii/S0021979714000708

That makes me wonder why so many inks are acidic, not sure it is because many typical dyes have nicer colors at low pH, or because of some reaction with the paper.

 

Xanthates are most likely not stable in acidic media. They might decompose forming CS₂, so it would be a very bad idea to add any xanthate to a non-alkaline ink.

The viscose process uses something similar, cellulose is mixed with CS₂ in an alkaline solution, forming a xanthate, which is then injected into an acid bath to turn it back into cellulose.

 

I looked at other reagents that could help, one I found is diethyl dithiophosphinic acid, which is supposed to be stable in strong acids [2], cited in [1].

 

This is just something I found online, I have zero experience with flotation reagents, and I don't know which properties would make it work in the ink.

 

 

https://imgur.com/CV4JHdn

 

[1] https://doi.org/10.1007/s42461-018-0039-1

[2] 10.1016/j.jmrt.2014.12.003

[3] https://pubs.acs.org/doi/abs/10.1021/ac60190a034

 

[3] has these amazing diagrams, that show how different acid concentration affect the performance:

 

 

 

[ferrogallic]

  On 10/29/2023 at 8:56 AM, InesF said:

  On 10/26/2023 at 5:33 PM, ferrogallic said:

At the concentrations mentioned in the patent (0.02%, mmol/l), [...]

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Here the patent is, as so many others are, vague! 0.02% is MUCH different from 40 mmol/l. Derivatisation of xanthan may break some bondings in the polymer chain. The molecular weight may still be high and 20 or 40 mmol/l may be an almost solidified mixture. Xanthan is thixotropic, that means its viscosity is reduced during stirring (or during flow). ... ➝ 

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sorry, that was my mistake being unclear. When I saw in the patent that the xanthate increases the wetting angle, I was very surprised, because xanthates are known to drastically decrease the surface tension, and this would certainly be an unexpected result.

Here is the plot from Witt's paper that has the exact substance from the patent (IV):

 

But, as you mentioned, 0.02% is a very small amount, and according to this plot the surface tension wouldn't change substantially.

 

It is not surprising that such small concentrations are effective, the xanthate (not xanthan, the polysaccharide), looks like something that would very strongly bind to metals:

 

So what is happening is that this compound binds to the nib, and makes it more hydrophobic. The surface tension of the ink is not changed much, and it doesn't react with the paper either.

 

But it only works in alkaline ink, in acidic ink it would form carbon disulfide and carbonyl sulfide, two very toxic compounds.

 

 

 

[txomsy]

  On 10/29/2023 at 4:30 PM, ferrogallic said:

So what is happening is that this compound binds to the nib, and makes it more hydrophobic. The surface tension of the ink is not changed much, and it doesn't react with the paper either.

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I wouldn't know for sure, but it is plausible, and the reason I said

 

  On 10/27/2023 at 10:09 AM, txomsy said:

Plus, charged surfaces may attract oppositely charged ink components (forming films or clogging) also changing their behavior.

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Even without the hydrophobic side chain, an ion that binds a metal surface may ease the flow of a polar fluid by countering its charge.

 

But all this is assuming we talk of an abstract fluid. Ink may be a solution, or a suspension, or both, and contain many components, some of which may be charged one way and some other; some may induce or neutralize charges in metals, others may bind to those metal surfaces, others may increase viscosity, others may be hydrophobic, amphoteric, etc... and we are only talking of ink-metal: plastics will exhibit different effects.

 

That is why there was -and still is- so much research on ink formulations: the problem has many variables and its complexity allows for a rich set of interactions among all the different components.

 

 

Another factor is surface tension. I think at times we may be confounding the terminology: some times it is used as a generic term reflecting cohesiveness of a fluid (an inherent property of the fluid) and some times as a measure of its behavior in the air-fluid interface only -reserving the wetting angle for the fluid-solid interface (a property depending on both interface components).

 

Again, we can think of ink as a mixture of "fluids" and having properties that are the result of the properties of all its components plus the interactions between them. And while feeds are usually made in a single material, nibs are alloys composed also of several metals in varying proportions and with different properties (e.g. some will stain or corrode more easily than others).

 

Anyway, pH indeed affects surface tension and wetting angle, it is only that for some substances it is less influential (as for water) than for others. Water has many "unusual" properties, like a high "buffering" power (for pH, temperature, etc..). But ink may contain many additional ingredients.

 

All in all, it takes back to the same conclusion: the patent is for a maker who wants an ink that works well in pens made with a specific plastic and alloy combination that they think benefits from alkaline inks. Pens where BSB would be an ideal ink. And please, note that BSB will still work well in most pens, it is the staining and mixing properties that give it its bad name.

 

If one looks for more general recommendations, one would need to take a different approach, abstract, or ignore, or average as much as possible the ink-channel and nib properties (or accept that there will be unavoidable variations) and look for general solutions that affect mainly the properties of the ink.

 

I think that is what current makers of safe inks do: they assume different pens will use different plastics/resins/whatever ink channel compounds, that there will be no uniformity in nib alloys either, that tipping is also variable, and that there will be a large variety of papers.

 

So they aim for neutral pH inks, which will fall in the middle, may not match what acidic- or alkaline-loving pen materials need. but will not be too (extremely) far from any, and do the same with other properties: this may give "boring" inks, but inks that can be expected to work well in almost every pen and with most papers.

 

Then boutique ink makers try to push this or that property to optimize some behavior, only instead of optimizing for a specific pen make, they do for a specific property: color, wetness, shadowing, saturation, feathering, ghosting, whatever...

 

And that is what most aficionados should realize: if you want to be safe you need to either use an ink specifically designed for you pen (usually by the pen maker), an ink that just matches by chance your pen or a "boring", standard ink (the classics from Waterman, Pelikan, Parker, Montblanc...).

 

Any other ink (boutique or by a different pen brand) may (most likely) or may not (most unlikely) work; A boutique ink will most likely fall within the allowances of a given (your/one of your) pen model(s) or may fall short by a small bit and demand some minor extra maintenance; and the only way to know is by trying it (or reading reviews as I said above).

 

Nothing serious or to worry about: one only needs to remember that inks are complex formulations, that there are "safe" inks and "specialized" inks, and that the later may misbehave; so one only needs to watch out if any given ink shows any deviation in any given pen and in that case simply take a little extra care to not leave the pen unused for too long (and to flush pens when switching inks).

 

That said, I often have pens inked and unused for months. So, in my most humble opinion there is no need to get paranoid about FP inks and pens (except may be for some odd exception*).**

 

* Not mixing acidic with basic inks is one case to remember: they will form salts and my end clogging your pen (usually not immediately, but in the long run, they may); or not using strongly reactive alkaline inks (e.g. BSB) with susceptibly reactive negatively charged plastics (e.g. some sacs/feeds): they may dissolve (like dissolves like), again, usually not immediately (there may always be extreme exceptions), but in the long run, they may. If in doubt, or if you prefer to err on the cautious side, then, please, stick to safe inks.

 

** Please note the words in bold, specially the underscored one.

[LizEF]

[InesF]

  On 10/29/2023 at 4:30 PM, ferrogallic said:

When I saw in the patent that the xanthate increases the wetting angle, I was very surprised, because xanthates are known to drastically decrease the surface tension, and this would certainly be an unexpected result.

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Oh, my! 😱 Indeed, I didn't read carefully and three times I read xanthane and not xanthate. Sorry, for my sloppiness!

 

The substance with the structure formula as shown must have a negative RedOx potential. Means: it will react with oxygen (maybe catalysed by metal surfaces) and it will, most probably, react with the usual dyes of fountain pen inks. When it was/is used as described in the paper of the Chinese scientists, its application was optimized for metal extraction (building complexes with multivalent metals, dissolving them from minerals).

Whatever the solutions of this substance do with surface tension and/or viscosity is meaningless (and useless) for fountain pen inks because of its reactivity and because of its toxicity.

[InesF]

  On 10/29/2023 at 7:03 PM, LizEF said:

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I love how you are able to direct this orchestra!  

[LizEF]

  On 10/29/2023 at 7:50 PM, InesF said:

I love how you are able to direct this orchestra!  

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That was supposed to be me throwing my hands up in despair at ever understanding the discussion...

[inkstainedruth]

  On 10/29/2023 at 7:03 PM, LizEF said:

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@InesF -- I don't think she's conducting so much as throwing up her hands going "I give up!"  Which is about where I am at this point....  I never took physics and I hated high school chemistry (I had to re-arrange my entire schedule because they didn't schedule me in a math class -- let alone the one I was SUPPOSED to have been in; so I ended up having chemistry at the end of the day, in a class that only had two other girls in it, and a lot of the boys had just gotten out of gym so they were all sweaty and gross....  Plus the chemistry teacher was a jerk....

Ruth Morrisson aka inkstainedruth