Athos saw this in a magazine and had to try it. The effect was quite nifty so I thought I would share it here.
Ours isn’t much of a lemon juice kitchen so we had to go out and get some. I squeezed the juice out, strained out the pulp and seeds, gave the kids some brushes, and let them have a go at writing and drawing whatever they wanted.
The tricky bit is getting used to the idea of drawing without seeing anything. The natural response is to keep adding more juice, just in case, creating a very wet piece of work.
In any case, the result is wholly invisible. Let it dry, and if you want you can even get the kids to write over the paper to enhance the “secret message” effect.