For nerdy youngsters, writing secret messages with lemon juice is an age-old tradition. 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 technique which is way cooler than using lemon juice. It uses turmeric. This isn’t like the invisible ink of our childhood.
That’s probably a good thing. It’s unlikely that an LED bulb will generate enough heat for our secret messages. [Ranomona’s] ink doesn’t use heat, but it uses a developer. You must prepare both the ink as well as the developer. As you can see in the below video, however, they are still amazing.
The principle relies on turmeric’s ability to act like litmus paper. It turns red when it comes into contact with alkalis. Acid makes the ink yellow. Ink is then any viscous, alkaline substance. You can, for example. [Randomona] Use either washing powder or baking soda mixed with water. Your secret will be safe once it dries.
As a development agent, turmeric and alcohol are used. Alcohol is used in hand sanitizer. You can get away with water, too, but the results won’t be nearly as impressive. The rest of the project is just arts and crafts. In the post, there are several cool ideas. One of them is to use a yellow pen and paint with developer on a plain message.
It’s a fun project you can do with your child, particularly if they 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 much 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.