Want to pass notes in school and avoid detention? Here's the perfect solution, invisible ink! You can make invisible ink out of a surprising number of common household ingredients. Write on paper with these substances and then expose them to heat, like an iron. Just be careful not to set the paper on fire! You should see the words magically appear. I tested a few and here are my results:
Milk - This one worked pretty well. The message doesn't come in very dark but it is legible.
Lemon Juice - This was the least successful. I couldn't see it on the paper when it was dry but it took a long time of heating before it started to appear.
Sugar water solution - This one didn't work as well because the sugar water became shiny on the paper so someone could read it without heating.
Baking Soda and water solution - This one worked great. It was the first to show up and had a nice brown color.
Why does this work? Both milk and lemon juice contain proteins and sugars that undergo a series of chemical reactions called Mailliard reactions. This is when sugar molecules attach to protein molecules. This creates the browning on the message. For sugar when the molecules are heated they form longer chains that then tangle with each other. These chains absorb more blue light than the paper which then appears as brown.
A nice side effect is that my laundry room now smells like caramel.
Try your own invisible ink and post your discoveries in the comments below.