Invisible ink, also known as sympathetic ink, is a writing fluid that is invisible under normal conditions but can be revealed by heat, light, or chemical reaction. It has been used for centuries for secret communication, as it allows messages to be hidden in plain sight.
Invisible ink can be made from a variety of materials, including lemon juice, vinegar, and milk. To write with invisible ink, simply dip a pen or brush into the ink and write your message on paper. The message will be invisible until it is heated, exposed to light, or treated with a chemical reagent. This makes it an ideal way to send secret messages, as the message can be easily hidden from prying eyes.
