During the „I can be a Scientist” class, students learnt about the properties of various chemicals – iodine and lemon. The students at first started to ask themselves a few important questions: What happens when iodine is combined with starch? To what color will a pita bread change? What if we heat paper soaked in lemon juice? And above all, why are we learning about it? What use is it for us? The main aim of this class was to introduce old methods used to write a secret messages – Encryption. Playing as a detective and leading about the properties of various chemicals as well as chemical reactions ended with a complete success. Now, our know that iodine, when combined with starch, changes the pita bread violet. While and heated paper soaked in lemon juice darkens much faster than plain paper and therefore the hidden letters – in an encrypted message become well visible.