Why Lemon Juice Works As Invisible Ink.

in STEMGeekslast year

Lemon juice is a common invisible ink for kids. But do you know why it works?
Lemon juice contain carbon based compounds which soak into the fibers of the paper that you draw the message on. Compounds are substances that are created when there is a bond between two or more chemicals.
I drew a hive logo onto the paper with a brush {and lemon juice}.Then I let the paper completely dry until it looked completely blank. You could no longer see the hive logo I painted.
After I held a lighter up to the paper: You could clearly see the lines of the hive logo. Its a bit light: but its dark enough to physically read.

Here is a crude cartoon drawing of what is happening on a chemical level. When you heat up the paper: The complex carbon molecule breaks down and the carbon leaves; staining the paper slightly. This is physically why lemon juice works as invisible ink. The carbon molecules {stick people} are freed from the complex molecule {the jail bars in the middle} and rush out of the paper { the arrows}.

There are many chemical processes that you can write secret messages in. This is just one of the simplest and oldest secret writing technique. Did you know that German nationalist spies used lemon juice to write secret messages? All the way back in 600 A.D. Arabs used lemon juice in their organic ink. Aeneas Tacticus mentioned invisible ink in writings from 4th century B.C.