To keep on the the secret code track we started with the cipher wheel free download, I thought I would write a little post on creating your own invisible ink.
Lemon juice is the one we all learned about as kids, but really anything that is organic and clear (or nearly clear) can work. Milk and egg whites are examples of possible "inks." When using an organic material as your ink, the reader simply needs to heat the paper in order to reveal the message. The common manner is to use a match or lighter, but I find ironing the paper on low is the best way to read the entire message while reducing your fire risk.
Baking soda also works with this heat method. All you need to do is mist one part baking soda to one part water as your "ink" and heat to reveal the message. Another way to read a baking soda message is to brush the paper with grape juice and the words will appear in a different color. Very odd indeed.
Corn starch can also work when made into a mixture. This is a little bit of work, but interesting because the message can only be revealed with an iodine solution. Mix two tablespoons of cornstarch with 4 tsp water in a pan over medium hear. Boil until it is a smooth, thick consistency, almost like gravy. (Make sure not to burn it.) When ready, dip a toothpick or paintbrush into the corn starch mixture and write your message on a piece of paper. Allow the mixture to dry on the paper before folding it or attempting to read it with the iodine solution. To read the message, mix 1 part iodine to 10 parts water and brush the solution on the paper with a swab over the hidden message. The secret message will appear in purple.