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This "practice calligraphy" paper has a special coating that amplifies the contrast between light/dark when a wet brush is applied.

The physics behind this effect has been explained:

From my understanding the refractive index of the liquid and roughened surface should be as close as possible (Eg: Glycerol 1.4729, and PMMA 1.4896) in order to maximize this effect. But this Pilot paper works better than any of my trials.

Can anyone suggest how it's made, or what materials/chemistry would work best?

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  • $\begingroup$ My guess is the paper is a corporate secret. $\endgroup$
    – Carl Witthoft
    Apr 12, 2017 at 15:48
  • $\begingroup$ Yes I think so too. I suppose I would like to reverse engineer it. Can you suggest how I might do that? $\endgroup$
    – Edan
    Apr 13, 2017 at 23:59

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A thick paper and treated the same way you treat a catalyst bead to become porous so the surface area can get more light. From this if you use a thick clear uncoated paper and leave it a few seconds in a ultrasonic cleaner then leave it to dry.

Another idea is a non-toxic dye that changes color when placed in a water environment like a compound molecule that only associates when water is present, after it dries the compound breaks and the color fades. You could try with copper but be careful how you handle it because some ions are toxic.

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