Invisible ink is a writing fluid that’s invisible below regular situations however might be revealed by making use of warmth, mild, or a chemical reagent. It has been used for hundreds of years for secret communication, and it’s nonetheless used at this time for a wide range of functions, together with safety, espionage, and counterfeiting.
There are numerous totally different recipes for invisible ink, however the commonest components embrace lemon juice, vinegar, and milk. These liquids are invisible when they’re utilized to paper, however they are going to flip brown when they’re heated. One other common recipe for invisible ink makes use of an answer of copper sulfate and water. This answer is invisible when it’s utilized to paper, however it can flip blue when it’s uncovered to mild.
