Enhancement > indicator

Messages or pictures are drawn on absorbent paper using a variety of colourless solutions and allowed to dry, rendering them invisible. Subsequently spraying the paper with solutions that contain different reagents that react with one or more of the chemicals on the paper to produce colours reveals the messages or pictures.
 

A solution of acidified potassium manganate(VII) (‘red wine’) is poured into a set of glasses containing small (barely visible from a distance) amounts of different colourless solutions made up from barium chloride, sodium thiosulfate, sodium carbonate and sulfuric acid. As a result of the chemical reactions that occur, the ‘wine’ changes into ‘water’, ‘