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Kitchen Steganography with Turmeric [Hackaday]
It is a classic rite of passage for nerdy kids to write secret messages using lemon juice. 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] shares a different technique that seems to be way cooler than lemon juice using, of all things, turmeric. This isn’t like the invisible ink of our childhood.
That’s probably a good thing. We doubt an LED bulb makes enough heat to develop our old secret messages. [Ranomona’s] ink doesn’t use heat, but it uses a developer. That means you must make two preparations: the ink and the developer. The results are amazing, though, as shown in the video below.
The principle relies on turmeric’s ability to act like litmus paper. Normally yellow, it turns red in contact with alkalines. Adding acid makes it yellow again. The ink, then, is any sort of viscous alkaline. For example, [Randomona] uses either baking soda or washing powder mixed with a bit of water. Once dry, your secret is safe!
The idea is to use turmeric and alcohol as a developer. In this case, the alcohol is in the form of hand sanitizer. You can get away with water, too, but the results won’t be nearly as impressive. Once you have both solutions, the rest is all arts and crafts. The post has several ideas for neat projects, including using a yellow marker to create a message that transforms when painted with the developer.
A great project to share with a kid, especially one who might be interested in art or chemistry. 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.
This is probably easier than using a UV laser for secret writing. If you really want secret messages, maybe create an invisible QR code.