“Gel ink is viscous, but it’s not thick enough to prevent it from flowing. This means it can evaporate over time”<p>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).<p>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).<p>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).
Oh wow. Did not know that there was an ISO standard for pen refills: <a href="https://unsharpen.com/pen-refill-guide/" rel="nofollow">https://unsharpen.com/pen-refill-guide/</a>
That was interesting but<p>> These thickeners can range from particulate silica, alumina, titanium dioxide, or even powdered clay.<p>If it were any of those, I imagine the stopper would be hazy, unless the refractive index of the matrix were very close to the aggregate. Curiosity abounds, the mind boggles.<p>Might be a silicone (polydimethylsiloxane) based grease, with various silicone oxides and/or polymers as thickeners. Now I wanna take one apart.
They didn't really indicate why the end is sealed with a fluid as opposed to something physical. I suspect it's because flowing ink with a solid stopper would create a vacuum and quickly cease to function. A stopper is fluid and so can flow along with the ink. The space between the stopper and the shell is probably vented.