Invisible letter | lemon invisible ink

Hello everyone! Now as I'm at home for a week, I need to start fulfilling my summer list again! Here's another item, something I wanted to try for a long time. As you might have noticed I love exprimenting (recently I also made a pinhole camera that is currently in use). This experiment connects painting and waiting for the result in tension - two elements I like!
This is a graphic letter that only one person will understand. Secret code, you know. :)

Any kind of organic liquid would work as invisible ink: you migh use milk, vinegar or a juice. I used lemon juice and it was almost invisible when it was dry! The point is that the compounds of ink must burn quickr than paper and leave brown marks on paper. The drawing/text will appear after you hold the piece of paper over a candle for a while. 

What I've learned? The text/painting shouldn't be too detailed. Otherwise it might be too blurred. I recommend trying this for all of you as it's easy, quick and interesting!

Have a beautiful day,
Julia