An alternative look at ink wetness

[RJS]

  On 8/8/2021 at 6:17 PM, LizEF said:

Please keep in mind that flow (wetness) is not the same as lubrication, and while wetter inks are often better lubricated (and drier inks often more poorly lubricated), that is not always the case.  I suspect:

1. Increased flow can improve lubrication, even without a lubricant
2. Decreased flow can reduce lubrication, even with a lubricant
3. (Some?) lubricants may lower surface tension, thus making an ink wetter

...but...

1. I don't know that all lubricants (I assume there are multiple possible lubricants for inks) lower surface tension.  (Technically, I don't know that any do this, I just suspect it.)
2. Even if a lubricant does lower surface tension, it's possible that the surface tension was high enough before addition that the ink still seems "dry" after the lubricant is added (thus, a dry, well-lubricated ink).
3. It's possible that surface tension is already low enough that the ink flows well without a lubricant - thus giving us a wet but "scratchy" ink (which may be mistaken for a "dry" ink).

It took me a long time of using many inks in the same nib on the same paper before I was able to determine that flow and lubrication are independent from each other.  And even now, it's difficult for me to always trust what I'm sensing, since it's subtle and utterly subjective.  (Some days I really, really wish I had a lab, training, and equipment to measure everything scientifically so I could compare facts to my writing experience, but none of that is going to happen, so I'll just have to stick with wizards, sphinxes, and a subjective EF  experience.  I also wish I could start over with what I know now, but there's no way I'm re-doing all those inks, and even if I did, by the time I was done, I'd have enough knowledge to want to start over yet again, ink reviews without end...)

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I agree that wetness and lubrication are different things, I just wanted to include the detail about one ink feeling lubricated while the other felt chalky, if that had any bearing on why the ink with low surface tension wasn't laying down as much ink as the other.

 

(Will reply to the rest of the message shortly, just got to pop out to get some urgent dinner ingredients now before I get scolded 😂)

[LizEF]

  On 8/8/2021 at 6:29 PM, RJS said:

I agree that wetness and lubrication are different things, I just wanted to include the detail about one ink feeling lubricated while the other felt chalky, if that had any bearing on why the ink with low surface tension wasn't laying down as much ink as the other.

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Gotcha - mistook the intent, but I get it now.

 

  On 8/8/2021 at 6:29 PM, RJS said:

(Will reply to the rest of the message shortly, just got to pop out to get some urgent dinner ingredients now before I get scolded 😂)

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Wouldn't want to to get scolded, scalded, or sent to bed without your dinner!

[RJS]

  On 8/8/2021 at 6:32 PM, LizEF said:

Gotcha - mistook the intent, but I get it now.

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I wasn't very clear, so I see why you took it that way.

 

  Quote

Wouldn't want to to get scolded, scalded, or sent to bed without your dinner!

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My credit card and I went for a little drive, thus avoiding any scolding, scalding or hungry/peeved family members. 😁👍

 

Regarding ink wetness- for me wetness is all about an ink's willingness to disembark its cozy home inside my fountain pen and set up camp on the paper. Specifically on fancy coated paper, as that's what I write on. Some pens seem wet regardless of ink, and some inks seem wet regardless of the pen. I tend to tweak pens to increase their flow, unless I use that pen for green ink and annotating printouts. I wouldn't tend to pair a wet ink with a wet pen, because there can be too much of a good thing, and I'd rather avoid bleed through/feathering/ridiculous dry times.

[InesF]

  On 8/8/2021 at 5:18 PM, RJS said:

Hmm, the ink wetness definition you find throws up some questions. For example, I tested Waterman Serenity Blue (very high surface tension) and R&K Scabiosa (very low surface tension) in the same pen on the same paper. Serenity Blue laid down a lot of ink and felt extremely well lubricated, while Scabiosa laid down substantially less ink and felt as dry and chalky as an ink can feel. In this one instance it would appear that surface tension doesn't play a prominent role in wetness. Maybe the Scabiosa disliked the combination of a fairly broad and very smooth nib on coated paper?

 

Edit: The high surface tension of the Serenity Blue did show itself in terms of the ink pooling and drying slowly, and then showing considerable sheen.

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Thank you for sharing your observations!

 

That's surprising for me. In my tests with two pens on two paper types and with additional two pens, each on TR 52g/m2 paper, the Waterman came out dry in a finer line with some shading while the Scabiosa ran out of my nibs, feathered on absorbent paper and caused comparably thick lines. However, because most of the ink is rapidly sucked into the absorbent paper, even a wet ink looks flat and seems to behave dry.

I have to admit, that almost all inks look nice on TR paper with much less difference between high and low surface tension. And also from the diagrams you can see that the 'fountain pen friendly' paper had lower differences in ink delivery between high and low surface tension. Finally, the paper quality is also a major factor in this pen-ink-paper triumvirate.

 

And yes, Liz already mentioned, ink delivery is not equal to lubrication, unfortunately. (it would had been too simple, if so)

[InesF]

  On 8/8/2021 at 6:17 PM, LizEF said:

...but...

1. I don't know that all lubricants (I assume there are multiple possible lubricants for inks) lower surface tension.  (Technically, I don't know that any do this, I just suspect it.)
2. Even if a lubricant does lower surface tension, it's possible that the surface tension was high enough before addition that the ink still seems "dry" after the lubricant is added (thus, a dry, well-lubricated ink).
3. It's possible that surface tension is already low enough that the ink flows well without a lubricant - thus giving us a wet but "scratchy" ink (which may be mistaken for a "dry" ink).

It took me a long time of using many inks in the same nib on the same paper before I was able to determine that flow and lubrication are independent from each other.  And even now, it's difficult for me to always trust what I'm sensing, since it's subtle and utterly subjective.  (Some days I really, really wish I had a lab, training, and equipment to measure everything scientifically so I could compare facts to my writing experience, but none of that is going to happen, so I'll just have to stick with wizards, sphinxes, and a subjective EF  experience.  I also wish I could start over with what I know now, but there's no way I'm re-doing all those inks, and even if I did, by the time I was done, I'd have enough knowledge to want to start over yet again, ink reviews without end...)

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Unfortunately, lubricants are a wide field of substance classes and most ink producers have their 'small secrets'. That's generally OK. However, in most cases some poly-alcoholes, poly-esters or poly-ethers are used. Some of them decrease surface tension more, others less, some support keeping the colors in solutions, others help keeping pigment suspensions stable. I know about three lubricants that are used in some ink brands, but maybe I do not know the ca. 30 others.

 

If you like to make an ink more wet, try to use one of the ready available ink lubricants, which contain Triton X-100. But do not use household dishwasher soap (or similar) - or do it once and learn the lesson.😜

 

  On 8/8/2021 at 6:20 PM, LizEF said:

Thank you, @InesF!  I really enjoyed this last update.  I now need to go review and see if you explained how to measure surface tension.  If it's easy enough, I think it would be fabulous for us to start gathering some sort of community-populated database of ink surface tensions.  (I suspect it's not so easy to do accurately, but still, I'm gonna go back and look.)

 

(And I'm now feeling kinda bad for An Ink Guy as I'm not so sure his massive work measuring ink viscosity gives us anything of use...  )

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Measuring surface tension of ink is the most easy of them. All you need is a calibrated and de-fated pipette. The more precise it is calibrated, the less the number of drops needed to be measured. That's all. Mine is calibrated for a precision of 0.02 mL, so I need to measure the volume of 10 free falling drops. You calibrate the pipette with water and with pure ethanol. And remember: each pipette is different, so if you break one, you need to calibrate the next and go on with the new function.

Do not use plastic pipettes, as they can deform (without you noticing).

 

As told already before, The Ink Guy did a combined measurement of surface tension and viscosity. As the viscosity has no effect on ink wetness (in normal viscosity range), he looses some sensitivity. But it doesn't mean his measurements are wrong. His form of data presentation doesn't have absolute values, they are all relative to each other. Again, not wrong, but you do not get out more details than the general classification he does.

And yes, the work he did is massive - I have a lot of respect for his effort!

[LizEF]

Thanks again, InesF!  Good info.  I didn't realize An Ink Guy's test included both - I probably missed something the first time through.  Regarding this:

 

  On 8/9/2021 at 12:26 PM, InesF said:

And remember: each pipette is different, so if you break one, you need to calibrate the next and go on with the new function.

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I'm well aware of this.  One of the applications I wrote for the microbiology lab I worked at (in IT) was to capture logbook data.  The two primary logbooks were the balance and pipette calibration logbooks.  Each person to use a pipette had to log calibration data at the start of their shift.  As it was explained to me, it was at least as much about calibrating the analyst (to ensure they could pipette accurately) as it was about calibrating the pipette!

[RJS]

  On 8/9/2021 at 12:03 PM, InesF said:

Thank you for sharing your observations!

 

That's surprising for me. In my tests with two pens on two paper types and with additional two pens, each on TR 52g/m2 paper, the Waterman came out dry in a finer line with some shading while the Scabiosa ran out of my nibs, feathered on absorbent paper and caused comparably thick lines. However, because most of the ink is rapidly sucked into the absorbent paper, even a wet ink looks flat and seems to behave dry.

I have to admit, that almost all inks look nice on TR paper with much less difference between high and low surface tension. And also from the diagrams you can see that the 'fountain pen friendly' paper had lower differences in ink delivery between high and low surface tension. Finally, the paper quality is also a major factor in this pen-ink-paper triumvirate.

 

And yes, Liz already mentioned, ink delivery is not equal to lubrication, unfortunately. (it would had been too simple, if so)

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Thanks for your reply. The Scabiosa was indeed very wet on cheap copy paper. It was with TR and Clairefontaine that it seemed reluctant. I wondered if perhaps a toothy nib rather than a super smooth one would have changed things. The paper, like you mention, levels the playing field for inks, with coated paper displaying nothing like the disparity you get between wet and dry inks on absorbent paper. 

[PithyProlix]

  On 8/8/2021 at 4:19 PM, InesF said:

Vacation was nice, but it's over now - time for a data update.

 

A total of 49 inks are measured now for surface tension, viscosity and pH-value. 16 of them were written with two different pens at two (sometimes 3) different papers types with measuring ink consumption per line length, line width and ink per paper surface area was calculated.

Some of the inks may be exotic for your region, however, only Ferris Wheel Press and Colorverse are the exotics in my region (besides some of the limited edition inks). All the other are quite commonly available for me, most of them are always on stock in the local shops.

 

This is the condensed analysis data table, colored and sorted as before.

Oh, I see, I didn't match the pH colors exactly. The two J.Herbin shimmering inks were measured without particles - I took the supernatant ink after letting it settle for a while.

Please remember, inks with addition of Gum Arabic (G.A.) were trimmed for calligraphy use. However, they behave still quite nice in my fountain pens!

 

Instead of the extended data table, here the graphical presentation of the writing data.

 

Correlation coefficients are not so high. Considering all measurement uncertainties, however, they are not that bad either.

 

And then I tried to combine the data for both pens (you remember, I did not before, because they have slightly different tip sizes) for the ink consumption per line length and per area:

 

OK, that was a bit a surprise. The correlation coefficient improved with the increased number of data points and, all of a sudden, outliers became visible (in the ellipses). But one after the other:

Still valid: surface tension is the most important ink property determining its wetness - the lower it is, the wetter an ink.

Still valid: the paper type plays an important role - absorbent (low quality) paper increases line width, feathering, spreading and bleeding and increases the amount of ink which is laid down compared to 'fountain pen friendly' paper.

Still valid: ink viscosity has no effect on ink wetness (as long as the ink is able to flow through the capillaries - and even the most viscous ink did flow quite nicely through both my pens).

New insight: the amount of ink laid down per area (line length times line width) followed similar rules for both the tested paper types (parallel correlation lines). As the inks spread out on absorbent paper not only in two but in three dimensions (sucked into the paper), the total ink delivery was still higher than it was on non-absorbent paper.

Outlier identified: in the current data set the clear outliers are the data points from the only alkaline ink (Iroshizuko) - clearly outside measurement deviation. Other may be there but currently hidden in the data point cloud.

New hypothesis: alkaline inks may interfere with the paper a bit differently than what can be predicted from its surface tension. The Iroshizuko ink has a low surface tension (which would suggest increased ink delivery) but the delivery amount was more in the range of mid to high surface tension inks, although it feathered and spread on absorbent paper! The consequence: I had to test more of the neutral and alkaline inks for the upcoming principal component analysis.

 

So far the news for this week, next update in ca. two weeks.

 

I'm open to discuss the data and still hoping you can see something that I missed! Thank you for reading!

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Wow, this is so cool! I started reading this thread in its first few days and decided to discontinue because I thought I might get too engaged.  But, curiosity won the day and I am back to reading it ...

So, forgive me if this has been asked before (because I have not reviewed the whole thread), but I wonder how much, if any, atmospheric conditions play a role, in particular air pressure, temperature, and humidity? And I'm also wondering about interaction effects, not only with atmospheric variables, but between the three variables you are measuring?

 

 Thanks for all the amazing work! You are a ⭐!

[PithyProlix]

Though not really directly related but seemingly of interest none-the-less is this recent journal article on how ink flows from a fountain pen and its design considerations: 

How the capillarity and ink-air flow govern the performance of a fountain pen

 

I don't have access to the full text (nor supplementary figures and even videos!) so I cannot write much more.

[InesF]

  On 8/9/2021 at 3:40 PM, RJS said:

I wondered if perhaps a toothy nib rather than a super smooth one would have changed things.

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Hi @RJS.

When I grind down a nib and test it in different process stages I observe increased ink delivery while the tip is still rough and a subjectively dryer behaviour after it is polished. Please keep in mind, this is an observation and not the result of systematic experiments.

Unfortunately, this is all I can tell about.

[InesF]

  On 8/14/2021 at 9:27 AM, PithyProlix said:

but I wonder how much, if any, atmospheric conditions play a role, in particular air pressure, temperature, and humidity? And I'm also wondering about interaction effects, not only with atmospheric variables, but between the three variables you are measuring?

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Hi @PithyProlix, you're welcome.

I cannot tell anything about temperature and air pressure, except for the obvious: when these change rapidly (sitting in the airplane, leaving a air conditioned room out into hot summer air), the air bubble in the cylinder/converter/cartridge will either expand or shrink. If it expands and the fountain pen is nib-down, ink will be sqeezed out. If the air shrinks, nothing really spectacular will happen until the pressure or temperature goes back to like before.

As long as temperature and air pressure are constant while you write, the fountain pen will function normally.

 

Humidity is a bit different. The paper will always absorb some water until an equilibrium between air humidity and paper aW (written: a index W; correlating with water content in the paper) is reached. High air humidity results in increased water content in the paper.

In high humidity, all inks will perform wetter than in low humidity. The effect will be way more pronounced for absorbent paper than for non-absorbent. You will experience more feathering and bleeding in humid air than in dry air and you will experienve longer drying times on all paper types.

[PithyProlix]

  On 8/15/2021 at 7:00 AM, InesF said:

As long as temperature and air pressure are constant while you write, the fountain pen will function normally.

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To make sure I understand, what do you mean by 'the fountain pen will function normally', please? Do you mean that in different temperatures or pressures (given they are constant, of course) that the fountain pen itself won't contribute to differences in flow?

Thanks for the detailed response!

[RJS]

  On 8/15/2021 at 6:46 AM, InesF said:

Hi @RJS.

When I grind down a nib and test it in different process stages I observe increased ink delivery while the tip is still rough and a subjectively dryer behaviour after it is polished. Please keep in mind, this is an observation and not the result of systematic experiments.

Unfortunately, this is all I can tell about.

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Thanks for your reply. It tallies with my experience of using nibs that come rough and smooth out of the box. The very smooth nibs tend to glide and seem to be frugal with their ink output, at least on the kinds of paper I use.

[InesF]

  On 8/15/2021 at 8:07 AM, PithyProlix said:

To make sure I understand, what do you mean by 'the fountain pen will function normally', please? Do you mean that in different temperatures or pressures (given they are constant, of course) that the fountain pen itself won't contribute to differences in flow?

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Hi @PithyProlix.

No, sorry, there is no hidden message.

I guess my English is not sufficient to explain without misunderstanding. What I meant is, a fountain pen will write at 30 degrees C with the same properties it does at 20 degrees C. Within the 'usual' range of temperatures nothing special will happen.

Problems may arrive when the pen warms up while you write with it. If the temperature change is small, the cavities in the feed will suck the ink, if the change is higher, your pen may loose a drop (or two) of ink.

[InesF]

Good morning.

It's time for another data update. Meanwhile 53 inks are measured for three of their properties and 20 of them have been used for the ink consumption (or delivery) test.

 

At first the condensed data table:

 

So far I have selected inks of different surface tension in the hope to get the most out of a correlation statistics. The slowly increasing data pool starts to allow identification of outliers and one of the first was the Iroshizuku ink which had significantly lower ink delivery than predicted from its surface tension. The special property of the Japanese ink is its high pH-value.

My now adapted measurement plan considers not only surface tension but also pH-value of inks, both to be distributed over the full range (of available inks). The next four inks therefore will be: Pelikan 4001 Brilliant Black, Pelikan 4001 Blue-Black, R&K Isatis tinctoria and deAtramentis Sherlock Holmes.

 

The data diagram is a helpful tool to visualize some of the putative dependencies and outliers.

The correlation between ink surface tension and ink delivery is, most probably, not a linear function. It looks more banana shaped (second order polynomic). Slightly alkaline inks tend to be drier than their surface tension suggest (dots in the blue ellipses) and strongly acidic inks tend to behave wetter (red ellipse). However, the set may not be free from imprecise measurements (grey ellipse; and others not identified yet).

 

A principal component analysis will be done as soon as the missing measurements with inks of medium surface tension (48 to 58 mN / m) and with inks from the full pH range are done.

 

The next data update will be done in two or three weeks.

 

[LizEF]

  On 8/22/2021 at 6:48 AM, InesF said:

The next data update will be done in two or three weeks.

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I'm on the edge of my seat!  (I probably won't stay there for 2-3 weeks because it would get uncomfortable, but I'll remain there figuratively.)

 

Thanks for the update.

[InesF]

  On 8/14/2021 at 9:44 AM, PithyProlix said:

Though not really directly related but seemingly of interest none-the-less is this recent journal article on how ink flows from a fountain pen and its design considerations: 

How the capillarity and ink-air flow govern the performance of a fountain pen

 

I don't have access to the full text (nor supplementary figures and even videos!) so I cannot write much more.

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The paper describes the pressure hysteresis in the ink capillary at the moment an air bubble is released from the air capillary into the reservoir - generally highly interesting at a theoretical level!

Although the authors consider surface tension of the ink (well done!), the article does not explain the general performance of a fountain pen. The authors describe an unsteady ink flow during the experiment - I think, there was something wrong with their pen.

[InesF]

  On 8/22/2021 at 5:58 PM, LizEF said:

I'm on the edge of my seat!  (I probably won't stay there for 2-3 weeks because it would get uncomfortable, but I'll remain there figuratively.)

 

Thanks for the update.

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Hi @LizEF, you're welcome!

 

Ha, ha, now you experience the same as I do while waiting for the next sequel of your wizard story! 

[LizEF]

  On 8/23/2021 at 1:09 PM, InesF said:

Ha, ha, now you experience the same as I do while waiting for the next sequel of your wizard story! 

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Touché.

[InesF]

A quick 'no-new-data' update.

 

I was sure having read a very good explanation earlier about why surface tension is the most important fountain pen ink property. But I lost the link and was unable to retrieve it until today.

It is Ravens March Fountain Pens site. You find the essence in paragraph 3 of the 'capillary action' chapter.

 

Combined with Amadeus W's site about fountain pen construction (it's an excellent read, I strongly recommend to read it all!), the pen-ink-paper-wetness-theory goes forward, step by step towards ultimate enlightenment.