3 ms·

“Gel ink is viscous, but it’s not thick enough to prevent it from flowing. This means it can evaporate over time” These are three different, unrelated phenomen

“Gel ink is viscous, but it’s not thick enough to prevent it from flowing. This means it can evaporate over time” These are three different, unrelated phenomena. In a Newtonian fluid, no matter how large the viscosity, the fluid will flow when a shear stress is applied (think honey). A gel is instead typically a non-Newtonian fluid, i.e. a certain threshold stress has to be reached before motion sets in (think toothpaste). I don’t really see why the author then relates evaporation to viscosity. Shielding the fluid of interest from mixing with the surroundings will prevent evaporation (close the bottle of water and it will remain full, leave it open and then it will evaporate eventually).

andreareina 5y ago
> (think honey) or even pitch: https://en.wikipedia.org/wiki/Pitch_drop_experiment https://en.wikipedia.org/wiki/Pitch_drop_experiment
- bernulli 5y ago
  My favorite least exciting experiment!
aqme28 5y ago
> Shielding the fluid of interest from mixing with the surroundings will prevent evaporation (close the bottle of water and it will remain full, leave it open and then it will evaporate eventually). If you close the other end, pressure will prevent the ink from flowing out the tip.
- bernulli 5y ago
  Maybe, if it’s not about a bottle of water where we don’t want anything to flow out, one could use some sort of Transparent Material At The End Of A Gel Pen Refill to close the plastic pipe and prevent exposure to air to prevent evaporation!
- zaarn 5y ago
  There is gas pressure pens that have a small amount of pressurize inert gas at the end instead, which means that those are in fact closed on the end and operate much longer due to no evaporation issues.
Broken_Hippo 5y ago
Thinner inks spread out in a thinner layer - I can stick a little ball of gel ink on a picture and even make a little texture in it, but this doesn't happen as well with thinner ink. The thinner layers have more surface area, making evaporation faster. You can see the effect with paint, too: Spray paint vs normal wall paint, for example. Also, when dehydrating fruits and vegetables, thin slices dry out faster (I know this isn't viscosity per se, but still with the surface area and thickness). I'm going to guess that there are other things at play here too (how water gets trapped, etc), but I really don't know the science behind it.
- bernulli 5y ago
  Good points - but here the ink is still trapped in its enclosure and we don't want it to spread at all when we're not writing.
  - Broken_Hippo 5y ago
    Speak for yourself - I use more ink for art than writing :) Realistically, though, this still happens when writing. The thinner ink puts out a thin layer of ink when you write: The gel ink builds up a little bit. You can make little lines in a pool of gel ink in ways you can't do with a regular ink pen. Different ink moves differently, even when it is in a pen.
    - bernulli 5y ago
      Haha, fair enough. But what I mean is that the whole discussion in the article is about ink that still in its compartment inside the pen, prior to writing/drawing/etc. It has nowhere to go and cannot spread.

andreareina 5y ago

> (think honey) or even pitch: https://en.wikipedia.org/wiki/Pitch_drop_experiment https://en.wikipedia.org/wiki/Pitch_drop_experiment

bernulli 5y ago
My favorite least exciting experiment!

aqme28 5y ago

> Shielding the fluid of interest from mixing with the surroundings will prevent evaporation (close the bottle of water and it will remain full, leave it open and then it will evaporate eventually). If you close the other end, pressure will prevent the ink from flowing out the tip.

bernulli 5y ago
Maybe, if it’s not about a bottle of water where we don’t want anything to flow out, one could use some sort of Transparent Material At The End Of A Gel Pen Refill to close the plastic pipe and prevent exposure to air to prevent evaporation!
zaarn 5y ago
There is gas pressure pens that have a small amount of pressurize inert gas at the end instead, which means that those are in fact closed on the end and operate much longer due to no evaporation issues.

Broken_Hippo 5y ago

Thinner inks spread out in a thinner layer - I can stick a little ball of gel ink on a picture and even make a little texture in it, but this doesn't happen as well with thinner ink. The thinner layers have more surface area, making evaporation faster. You can see the effect with paint, too: Spray paint vs normal wall paint, for example. Also, when dehydrating fruits and vegetables, thin slices dry out faster (I know this isn't viscosity per se, but still with the surface area and thickness). I'm going to guess that there are other things at play here too (how water gets trapped, etc), but I really don't know the science behind it.

bernulli 5y ago
Good points - but here the ink is still trapped in its enclosure and we don't want it to spread at all when we're not writing.
- Broken_Hippo 5y ago
  Speak for yourself - I use more ink for art than writing :) Realistically, though, this still happens when writing. The thinner ink puts out a thin layer of ink when you write: The gel ink builds up a little bit. You can make little lines in a pool of gel ink in ways you can't do with a regular ink pen. Different ink moves differently, even when it is in a pen.
  - bernulli 5y ago
    Haha, fair enough. But what I mean is that the whole discussion in the article is about ink that still in its compartment inside the pen, prior to writing/drawing/etc. It has nowhere to go and cannot spread.