Secret Message - Heat Friction Ink

Do you remember middle school, when you used to try to pass notes to your crush all the way across the classroom? You had butterflies in your stomach – until the teacher grabbed the note when it was between Jimmy and Suzy. Those butterflies immediately changed to fear. Note passing has since adapted. The teenagers of today have learned to use the technology at their disposal. And we aren't talking about text messaging either. This is much cooler... er... hotter.

The Covered-Up Message

1. Using the regular ink pen, write the message that you want your recipient to read.
2. Now, cover the secret message up with the friction pen.  Turn the letters into shapes or designs, scribble all over the words, or anything else that makes your secret message unreadable.

The "Flattering" Message

1. To make the flattering message work, you'll need a bit more time and you'll need to be really good with both of your pens.
2. Write a message that reads something like this:
   "Mrs. Williams is youthful and going to be, without a doubt and without a question, my most memorable teacher."
3. Make sure that the underlined parts are written with your regular ink pen, but write the rest with the friction pen.

Uncovering the Secret

1. When you have received a secret note that uses friction & heat ink, there are a number of different methods you can use to reveal the message.
2. Using a lighter is the quickest and easiest way, but always have an adult present when you use a lighter.
3. You can hold the message over the top of a toaster.
4. You can use a pencil eraser.  Just erase over the entire message.

Observations

What do you think makes the ink disappear, leaving only the normal ink behind?  What makes this form of secret message different from the other methods you have seen?

How does it work?

The friction pen uses ink that is sensitive to heat.  At temperatures that range between 15°F and 140°F, the ink will appear black when writing on paper.  But when local temperature exceeds 140°F, like when held near a heat source or when friction is concentrated on a certain spot, the ink becomes clear.  

This specially formulated ink is called thermochromic ink and can actually be formulated into different colors and to change color at different temperatures.  Believe it or not, this probably isn't the first time you've seen or used thermochromic ink.  This special ink has been used in mood rings and heat sensitive labels.  

Additional Info

Now, what if you spent an extraordinary amount of time disguising your secret message and your coverup ended up being quite the piece of art?  It's all right, your ink can come right back, making your coverup beautiful again.  Stick your secret message paper in the freezer!  Once the local temperature on the ink drops below 14°F, the ink will once again turn black.  Reappearing art!