We diluted some lemon juice with a little bit of water and then Defne used a cotton bud to draw/write using this mixture.
Apperantly she wasn't impressed as she just couldn't see what she was drawing! 
When she was finished I put the papers in the oven for maybe a minute or so ( the oven was already scorching hot as I was baking yummy pizzas)And then ....the magic happens!
if you look carefully, you will realize she tried to write her name. She loved it!The lemon juice is acidic so it weakens the paper.The acid remains in the paper after the juice has dried. When the paper is held near heat the acidic parts of the paper burn or turn brown before the rest of the paper does. You can try it with other acidic liquids like orange juice or vinegar, too.
I also LOVE The Artful Parent's version "Invisible ink with crayon resist",on my project list for the summer holidays.
Happily shared with The Play Academy, It's Playtime, Kids Get Crafty, Preschool Corner, and Tot School
