Fill a small bowl with lemon juice. Dip a cotton swab into the lemon juice, and use it to draw a picture or write a message on a blank sheet of paper. Use a toothpick dipped in the lemon juice to make fine lines. Use the lemon juice sparingly, because it will bleed on the paper and the message will be difficult to read. Wait a few minutes and let the lemon juice writing dry. Use a hair dryer to heat the paper, and the message or drawing will be revealed.
Use milk, vinegar or orange juice as appearing ink in place of lemon juice. Allow the paper to dry for a few minutes, and then use the hair dryer to heat the paper to reveal the message. This works because all of these liquids contain acid that remains on the paper after it dries, and the heat from the hair dryer burns the acid and turns it brown.
Mix 1/4 cup of baking soda and 1/4 cup of water in a small bowl. Fill another bowl with 1/4 cup of grape juice. Dip a cotton swab in the baking soda solution and use it to draw a picture or write a message on a blank sheet of paper. Wait a few minutes for the paper to dry. Dip a small paintbrush in the grape juice and paint it across the paper to reveal the picture or message. This method works because baking soda is a base and grape juice contains acid; a chemical reaction occurs when the base neutralizes the acid.