Simple Way to Return Invisible Images

Originally written by Lauren Sigfusson and published at

A New Twist on Invisible Ink

With many of us spending our time online, we tend to be laser-focused on preventing our personal information from falling into the hands of nefarious hackers. But let’s not forget about the security of print-based communications.

Remember how the ink appears and disappears on the Marauder’s Map that appears in Harry Potter and the Prisoner of Azkaban? Basically, scientists are trying to recreate this bit of magic to protect information. But instead of using a password to make the invisible ink show and vanish, researchers are using a simple chemical reaction.

In a study released Tuesday in Nature Communications, a group of scientists showcased that lead-based ink can be reversibly made invisible with salt. Using an inkjet printer and a customized ink cartridge, researchers printed images and writing onto parchment paper. The paper comes out as though nothing has been printed; UV and ambient lights also don’t show anything. But add a bit of halide salt and what’s printed quickly appears under UV light. Add more salt, and voila, it’s gone.

Other luminescent materials that could be turned off and on have been explored in the past, according to the study, but the drawbacks outweighed the benefits. Plus, they weren’t actually invisible in their “off” state — ambient or UV light easily made that ink appear. Yeah, not the safest.

While this new method shows promise, using lead as the decryption method is dubious given it’s toxicity. However, the scientists point out there could be an alternative to lead because several studies have indicated with non-toxic tin could also do the trick.

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