Andrew wanted to do a science experiment so I found one of my many thrifted science experiment idea books for one that was quick and one that I had all the materials for.
All you need for this one is a candle, lighter, vinegar, paper and some paintbrushes. The kids painted on their paper with the vinegar. This was their "secret code". Once it dried I put the outlined picture or letters over a candle flame. It's kind of dangerous considering I caught the paper on fire twice but I have pretty good blowing a fire out skills so it was okay. The vinegar changes the chemical composition of the paper so that those places singe faster than the rest of the paper, thus the "secret code" shows up!