Two methods of making secret messages with invisible ink are explained below.
Method #1 - Dip a small brush, stick, or toothpick in milk. Write your message on a piece of paper. Rub ashes, makeup (blush), or pencil shavings to reveal the secret message.
Method #2 - Take a white crayon or candle and write your message on a white piece of paper. Then paint the message with a dark color. The message will be revealed since the paint will not stick to the waxy writing of the crayon.