Imagine that you have received a note from a friend, or perhaps, intercepted a message from an enemy. But the paper appears to be blank. Well, fear not. If the message is written in disappearing ink, a few simple steps can reveal the hidden communication.
Apply heat to the paper. Use a 100 watt light bulb, an iron or a blow dryer. If the disappearing ink is an acidic or organic substance such as lemon juice or milk, the paper will burn at a different rate than the ink, revealing the spots where the secret ink lies.
Apply a chemical reagent such as lemon or grape juice with a brush, sponge or cotton swab. Experiment on a small portion of the page to see which reagent works best. For example, if the invisible ink is a baking soda solution, acidic grape juice will react with the sodium bicarbonate, revealing the message in a different colour. You can try apple juice, lemon juice, vinegar, grape juice, white wine and many other acids.
Rub salt into the disappearing ink. Wait a minute and then brush the salt off the paper. To reveal the message, write over the page with a wax crayon.
When heating the page, be careful not to ignite the paper. Do not use a halogen lamp because there is a greater fire hazard.