White crayon, white paper, water color paint, brush or sponge.
Write a message or draw a picture on the white paper using the white crayon. To see the message/drawing, brush or sponge water color paint over the entire paper. The wax from the crayon will repel the colour and the message will come through.
“Send as a secret message to a friend. Don’t forget to provide them with written instructions on how to reveal the message.”