For nerdy youngsters, writing secret messages with lemon juice is a rite of passage. If you somehow missed that, you can’t see the writing until you heat the paper up with, say, an old-fashioned light bulb. If you were a true budding spy, you’d write a boring normal letter with wide spacing and then fill in the blanks between the lines with your important secrets written in juice. This is a form of steganography — encoding secret messages by hiding them in plain sight. [Randomona] This technique, which uses, of all the things, turmeric, is a lot cooler than lemon. This isn’t like the invisible ink of our childhood.
That’s probably a good thing. We doubt that an LED bulb produces enough heat to create our old secret codes. [Ranomona’s] ink doesn’t use heat, but it uses a developer. This means that you have to prepare two things: the ink, and the developer. As you can see in the video, however, the results are stunning.
The principle relies on turmeric’s ability to act like litmus paper. Normally yellow, turmeric turns red upon contact with alkalis. Acid makes it yellow. Ink is then any viscous alkaline. As an example, [Randomona] You can use either washing powder or a little baking soda. Once dried, your secret will be safe.
It is possible to create a pigment by mixing turmeric with alcohol. The alcohol used in this instance is found in hand sanitizer. You can get away with water, too, but the results won’t be nearly as impressive. The rest is just arts and crafts. This article has several cool ideas for projects. One of them is to use a yellow paint marker to create an image that changes when you add developer.
This is a great project to do with kids, especially those who are interested in chemistry or art. We don’t suggest writing your passwords with washing powder, but we wondered if we could hack an inkjet printer to produce blank pages of secret messages.
It’s probably easier to use this method than a UV-laser for secret writing. You can create an invisible QR Code if you want to send secret messages.