TITLE: What is the mechanism behind Wet Surface Writing Pens?
QUESTION [0 upvotes]: I came across pens/markers Eg- here and here  which can write on a wet surface. I want to know the mechanism behind them- their ink, or the delivery system, their nibs.
I need these information for a project I am working on.
Also I am not sure if this is the correct site to post this question, kindly let me know which will be the best site to ask this.

REPLY [1 votes]: To add to Jon Custer's comment, the space pens that operate underwater are pressurized to about 45 psi and have a special viscoelastic ink.

Once the ink is in contact with the surface, it needs to be non-soulable in water, so an alchohol as a solvent is helpful. The viscoelasticity is also helpful because once the ink is out of the pen the viscosity is increased helping keep the ink together in place on the surface.
For other markers that don't use the pressure and viscosity trick, it is probably most probably needing to choose an ink that is not soluble in the water, but still "drys" under water.  You can also buy inks and pens that are not soluble in alcohol or other common solvents.
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