Invisible ink is a writing fluid that is invisible when applied to paper but can be revealed later by heat, light, or chemical reaction. It has been used for centuries to send secret messages, and it is still used today for a variety of purposes, including security, espionage, and entertainment.
One of the most common ways to make invisible ink is to use lemon juice. Simply write your message on a piece of paper with a lemon wedge, and allow the juice to dry completely. The message will be invisible until it is heated, at which point the lemon juice will caramelize and turn brown, revealing the message.
