I have read when i was in fourth grade that onion juice could be used to make invisible ink that appears when the paper is heated.
There was also a scene[0] in National Treasure film (2004) where they use lemon and heat to reveal a hidden text
There was also a scene[0] in National Treasure film (2004) where they use lemon and heat to reveal a hidden text
I’m curious about how it bends the paper. The retractile nature of drying juices must create visible irregularities on the surface.