Invisible ink is back, and it’s better at hiding than ever. A new invisible ink that you can print is harder to reveal than most common cyphers.
Liang Li at Shanghai Jiao Tong University in China and his colleagues created this new ink accidentally while trying to synthesise a kind of glowing nanomaterial. In the process, they created a lead compound that was invisible to the human eye.
When a mixture of a particular kind of salts was applied, the text became visible again. Without these salts, no one would suspect anything was on the page.
It’s so much better than just using lemon juice. Most of the invisible inks we use now leave a residue behind as they become legible. This means that decrypting the message can be as easy as holding it up to a light. This compound can also be printed with a modified office printer, making it easy to fabricate a covert letter.
While it may seem antiquated or like a useless party trick, invisible ink can actually be used in anti-counterfeiting measures. United States currency uses a variation on invisible ink to hide text or pictures on large denominations of money so that they’re only visible in certain light.
“This invisible ink can be used to record and protect confidential information by printing process,” Li says. He says that it could also be useful in devices that combine light with electronics. For instance, using these types of compounds in a television or tablet screen could lead to richer colours – the team’s original motivation for studying them.
However, there are downsides. Lead is toxic, so the sender or recipient could end up harmed by the message. The team is exploring the possibility of swapping out the lead for tin, which is vastly less toxic.
Li Tan at the University of Nebraska-Lincoln says the compound is also known to dissolve in small amounts of water. The lead compound itself might also break down after repeated usages.
“The work itself is solid, no doubt about it,” Tan says. “The question is, how many times can you use it?”
Even if it only works once, this mixture could be among the best ways to send a secret message — as long as researchers are able to make sure it won’t poison the recipient.
Read more: Stretchy plastics hide secret pictures
Journal reference: Nature Communications, DOI: 10.1038/s41467-017-01248-2