Invisible ink is a writing fluid that’s invisible below regular circumstances however could 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 a lot of completely different recipes for invisible ink, however the most typical substances embrace lemon juice, vinegar, and milk. These liquids are invisible when they’re utilized to paper, however they’ll flip brown when they’re heated. One other fashionable 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’ll flip blue when it’s uncovered to mild.
