Lemon juice is used to create secret messages by nerdy children. 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 much 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. You must prepare both the ink as well as the developer. However, as you can see from the video below, it produces some amazing results.
The principle relies on turmeric’s ability to act like litmus paper. Normally yellow, turmeric turns red upon contact with alkalines. Addition of acid turns it back yellow. Ink can be any type of viscous acid. You can, for example. [Randomona] You can use either washing powder or baking soap mixed with some water. Once your secret has dried, it is safe.
It is possible to create a pigment by mixing turmeric with alcohol. In this instance, the alcohol comes in the form hand sanitizer. You can get away with water, too, but the results won’t be nearly as impressive. After you’ve got both solutions, it’s all about arts and craft. This post contains several neat ideas, such as using a yellow pen to create a message which transforms into a picture when you paint it with developer.
This is a great project to do with kids, especially those who are interested in art and 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.
It’s probably easier to use this method than a UV-laser for secret writing. You can create a QR code if you want to send secret messages.