Materials:

• small containers - 1 for each liquid
• lemon, orange, or grapefruit juice, milk, baking soda solution, or sugar solution
• cotton swab
• sheet of white paper
• electric iron (or 150 watt electric lamp or pop-up toaster)
• insulated mitts or hot pads
• Cloth towels

Instructions:

1. Add a little of each liquid to the small containers, one container for each liquid. To make the baking soda and sugar solution: Add a pinch of baking soda to an ounce of warm water in the small cup. Mix well. Add more baking soda a pinch at a time until the liquid is saturated (cannot hold any more baking soda). Follow the same instructions for the sugar solution.
2. Place a piece of white paper on your table. Dip a cotton swab into one of the “inks” (lemon, orange, or grapefruit juice, milk, baking soda solution, or sugar solution). Write a message on the paper. Your message will be nearly invisible when it dries. How can we make your message easier to read?
3. What happens when you bake cookies too long?  They burn turning brown or black. We can “ bake” or “cook” our spy ink messages, which will allow us to see our secret messages. How can we “ bake” our messages? By heating the paper with an electric iron, we can make your message appear. CAUTION:  Do not use an open flame. Adult supervision is necessary so as not to burn your fingers. Predict how your message will look. What color is your message?

Science:

What do the spy inks have in common?

They are all found in your kitchen, and can be used in baking. The water in your inks evaporates, turn from liquid to vapor, leaving behind an almost invisible trace of chemicals (what was in the ink besides the water). This trace can be changed into something we can see by heating it with heat from the iron. Heat energy breaks and makes new chemicals come of which are now visible to our eyes.