Here is a way to use baking soda to make invisible ink.
Mix equal parts of water and baking soda. Use any instrument that
you choose to transfer your baking soda ink message to a plain piece of
paper. Allow the paper to dry. When you want to read your
secret message hold the paper to a heat source such as a light bulb.
The heat will cause the baking soda ink to turn brown. Another
method of reading your message would be to paint your paper with grape
juice. The message will turn to a different color.
