An alternative look at ink wetness

[txomsy]

Maybe because inks are often diluted solutions and it is usually expected that viscosity will not vary too much from one ink to another. Although with modern oversaturated inks that is now arguable.

[InesF]

Thank you, @dipper for the quick response. I fully agree.

 

5 hours ago, mtcn77 said:

Well, to complicate matters further, the differences can be elucidated if we compare oil and water: water has more surface tension than oil, but oil always flows slower(I think) since it has higher viscosity.

@mtcn77, the first and most important is to come free from the imagination of any form of flow regulated ink delivery in fountain pens.

In other words: a functional fountain pen is NOT flow limited.

[InesF]

24 minutes ago, txomsy said:

Although with modern oversaturated inks that is now arguable.

Among the most oversaturated (and maybe above average viscous) inks in my measurement set were Diamine Green-Black (viscosity 1.374 mPa*s) and deAtramentis Aubergine with Gum Arabic added (viscosity 1.233 mPa*s). These both had 20-30% higher viscosities than 95% of the others and were still far flow limited.

 

I do not know, I can only guess: flow limitation may start with a viscosity above 2 mPa*s - or not far from that. Ink manufacturer know that and will not release such an ink for fountain pens. (Only for calligraphy or for drawing!)

 

And again: a flow limited fountain pen is no fun! You will recognise immediately and chances are high you will hate it and/or send your pen for repair.

[arcfide]

On 6/15/2022 at 3:57 AM, InesF said:

a functional fountain pen is NOT flow limited.

 

Can you discuss the difference in your model between "flow limited" and different rates of flow between various fountain pen feeds? It seems to me that all fountain pen feeds limit the rate of flow to some level, and some seem to restrict this flow much more than others, which colloquially would make me think of all fountain pens as having a flow "limit" and thus being "flow limited", but I think you have a different technical meaning in mind when you say "flow limited?" 

[mtcn77]

8 hours ago, arcfide said:

 

Can you discuss the difference in your model between "flow limited" and different rates of flow between various fountain pen feeds? It seems to me that all fountain pen feeds limit the rate of flow to some level, and some seem to restrict this flow much more than others, which colloquially would make me think of all fountain pens as having a flow "limit" and thus being "flow limited", but I think you have a different technical meaning in mind when you say "flow limited?" 

I think we could do some tests since @InesF is kind enough to provide with all the necessary details.

It says here that capillary action takes the form of;

h=(2*T*cosθ)/(r*ρ*g)

Now in this context 'T' is the surface tension, the theta angle is related to the attractive 'polarity' forces between the materials(water will be attracted to polar surfaces and oil to apolar), r is the capillary tube container's inner radius, p is the given liquid's density and g is gravity.

It seems to me, we have just what we need to formulate regarding viscosity eventhough we can also deduce by looking at any ink's viscosity value by itself.

I'm not convinced though - aren't we looking for inks with low surface tension? Well, it says in the formula that surface tension increases capillary action. Perhaps this isn't such a straight forward proposition since detergents do the opposite what this formula expects them to do.

[dipper]

3 hours ago, mtcn77 said:

It says here that capillary action takes the form of;

h=(2*T*cosθ)/(r*ρ*g)

 

That equation gives the vertical height "h" to which a liquid will be drawn up inside a narrow tube with one end dipped into an open dish of liquid, and with the other tube end open. That is an interesting equation. (See Jurin's Law.)

 

But clearly a fountain pen is not "a narrow tube with one end dipped into ....".

 

Is the Jurin's law equation at all relevant to wetness?

The equation is relevant to ink flowing into a capillary-filler pen, when being filled by standing the pen's nib end in a bottle of ink.

But it does not really explain anything about how much ink comes out of a fountain pen when writing onto paper.

 

However, the wetness experiments reported in this forum topic are not directed at explaining wetness by theoretical models. (That is an interesting but entirely different question.)

 

The aim of the experiments was to measure a number of ink properties in a laboratory (density, pH, etc), for very many inks, and also measure actual ink wetnesses when used in a fountain pen drawing ink lines onto paper, and then compare the actual ink line wetnesses of each ink with the lab. measured properties of that ink.

The comparison of experimental results showed a clear inverse relationship between A ) an ink's wetnesses when used with a pen onto paper and B ) the ink's surface tension value as measured by laboratory methods.

 

The conclusions of the experiment present that finding more fully.

The experiment does not attemp to explain how or why that relationship comes to be so.

 

In scientific studies experimental results always trump theoretical models.

[txomsy]

And, in any case, that does not define flow or whether it is limited. It only adds one factor to the equation.

 

Flow will depend on several other factors too: anyone who has cleaned/flushed a pen has seen ink or water exit the nib at higher speeds when pressure is applied on the opposite end. So given enough pressure any channel will not be flow limited until it bursts.

 

But if we stick to writing conditions, I think that most pens are flow-limited: and an easy way to see it is to try to write nib up against gravity. Just like changing the gravity, changing the nib, for the same section/feed, may result in skips as the pen is unable to keep up with broader lines... or in blots if the pen delivers too much ink with thinner lines... for any pen.

 

That said, I just had an idea... if one were to change the design so that no air enters the pen (using a think plastic sac that shrinks as ink is delivered) and the channel had enough capillary force, then theoretically one should be able to write upside-down. It would require different nib, feed channel and ink design and materials to increase capillarity, and a balance to be reached to ensure ink only comes out as it is drawn by attraction by the paper. Maybe that would be easier with a ball-point pen.

[arcfide]

47 minutes ago, txomsy said:

theoretically one should be able to write upside-down

 

My fountains pens write upside down as they are. There is plenty enough capillary action for them to write upside down for as long as the feed has ink in it. Once that is used up, simply tipping the pen back down to pull in some more ink from the ink reservoir will allow for another feed's worth of writing. 

[dipper]

13 hours ago, txomsy said:

anyone who has cleaned/flushed a pen has seen ink or water exit the nib at higher speeds when pressure is applied on the opposite end. So given enough pressure any channel will not be flow limited until it bursts.

 

I think the intended meaning of "...pen is not flow limited..." in this forum topic is that ink flow rates, in normal pen use, are well below the maximum flow rate that the pen could deliver whilst maintaining a relatively uniform line wetness.

 

That "not-flow-limited" behaviour describes a good fountain pen. But some (bad) pens may indeed be "flow limited". Meaning if you write at anything faster than a snail's pace the lines become thin, spidery, and the (bad) pen starts skipping.

 

But in the experiments reported in this topic, the two pens used (a Cross and a Waterman), each with 80+ inks, and onto two paper types, it was an important early finding that at all moderate speeds the line wetness held constant. That allowed test measurements to be made laying down thousands of line of ink by hand, without requiring a pen-testing machine to move the pens at a precision controlled reference speed over the test papers.

 

Communicated to us by the phrase "the pens are not flow limited".

[arcfide]

2 hours ago, dipper said:

But in the experiments reported in this topic, the two pens used (a Cross and a Waterman), each with 80+ inks, and onto two paper types, it was an important early finding that at all moderate speeds the line wetness held constant.

 

I think that's helpful. I think, however, that it is very common to see variable rates of practical flow in a fountain pen even among "working" feeds. Especially when a feed is initially saturated, it's easy to see that a pen writes more wetly at first as the feed reaches a state of equilibrium, but I also have noted that many pens have a variable rate of flow over time when writing, which creates an ebb and flow. The pens will never go dry, but they will become slightly wetter and slightly drier during writing. This happens across brands, and especially with some inks over other inks, related, I am sure, to the surface tension and the readiness of an ink to allow air back into the ink chamber. 

[InesF]

On 6/16/2022 at 11:48 AM, arcfide said:

but I think you have a different technical meaning in mind when you say "flow limited?" 

Hi @arcfide.

My English doesn't allow to formulate more differentiated than: to my understanding, flow is the amount of liquid (ink) passing by during a certain time; and flow limited in the context of fountain pens is when less ink CAN arrive at the nib tip than is demanded (menas: during your handwriting you see less and less ink arriving at the paper over time).

 

[InesF]

On 6/18/2022 at 1:42 AM, dipper said:

But in the experiments reported in this topic, the two pens used (a Cross and a Waterman), each with 80+ inks, and onto two paper types, it was an important early finding that at all moderate speeds the line wetness held constant. That allowed test measurements to be made laying down thousands of line of ink by hand, without requiring a pen-testing machine to move the pens at a precision controlled reference speed over the test papers.

 

Communicated to us by the phrase "the pens are not flow limited".

Thank you, @dipper!

[mtcn77]

On 6/18/2022 at 2:42 AM, dipper said:

 

I think the intended meaning of "...pen is not flow limited..." in this forum topic is that ink flow rates, in normal pen use, are well below the maximum flow rate that the pen could deliver whilst maintaining a relatively uniform line wetness.

 

That "not-flow-limited" behaviour describes a good fountain pen. But some (bad) pens may indeed be "flow limited". Meaning if you write at anything faster than a snail's pace the lines become thin, spidery, and the (bad) pen starts skipping.

 

But in the experiments reported in this topic, the two pens used (a Cross and a Waterman), each with 80+ inks, and onto two paper types, it was an important early finding that at all moderate speeds the line wetness held constant. That allowed test measurements to be made laying down thousands of line of ink by hand, without requiring a pen-testing machine to move the pens at a precision controlled reference speed over the test papers.

 

Communicated to us by the phrase "the pens are not flow limited".

I'm glad such a conclusion came about, I must have overlooked if static ink expenditure has been stated during the experiments while making the prediction good nibs don't lay too much ink, they serve the same purpose after all.

PS: okay, not exactly in the same thread.

On 6/4/2022 at 9:48 PM, mtcn77 said:

I just got a brand new Kaweco broad nib. A slight update and a pointer that might sum up my experiences, I think ink bleedthrough really defines how good a nib is. Those with the least initial pressure to write don't bleedthrough and write instantly - at least after the initial occasional hardstart. Therefore, I think wetness is not as good a benchmark as bleedthrough.

[InesF]

For all of you still interested in the topic:

The manuscript about this alternative ink wetness theory is now published in Material and Design (← click here, the link points at the web view, you may download the PDF for offline reading).

 

The publication is open access: no paywall, no secret commercialisation of your private data! Please do not upload and share the PDF on other sites, every download is important for the Journal site and for the impact counting. Thank you for your understanding!

 

Have fun reading and thank you all for your support and discussion!

[LizEF]

2 hours ago, InesF said:

The manuscript about this alternative ink wetness theory is now published in Material and Design (← click here, the link points at the web view, you may download the PDF for offline reading).

Hooray!!  Congratulations!   I'm going to save this for early next week when I can dedicate time to it rather than rushing through - though I've already scrolled through and looked at the structure and such and it looks fabulous.  Very happy for you.  I'm looking forward to a deep dive on Monday.

[mtcn77]

Great work, @InesF! Normally, I would tread lightly in statistics heavy essays.

One thing came to mind: did flushing between inks become significant, did leftover water cause any ink dilution, have you checked for any variance in ink properties between the bottle versus in the pen?

[txomsy]

Great work, my most sincere congratulations.

[LizEF]

27 minutes ago, mtcn77 said:

One thing came to mind: did flushing between inks become significant, did leftover water cause any ink dilution, have you checked for any variance in ink properties between the bottle versus in the pen?

Read the beginning of the thread - Ines went to great lengths to ensure such things didn't influence results.

[txomsy]

Wow! it has an IF of 7.9!!! That's a helluva lot. Really impressive My most sincere congratulations squared (and cubed). That is quite am achievement and shows that FPs are way more interesting than most of us believe.

[mtcn77]

52 minutes ago, LizEF said:

Read the beginning of the thread - Ines went to great lengths to ensure such things didn't influence results.

We can have controls and limitations. I just don't know from a personal perspective that 48 hours gets the pens dry.