Effect: This trick creates the illusion of ink magically disappearing from a surface when subjected to heat, using a friction pen.
Materials:
A friction pen available at most stationery or magic supply stores.
A regular pen with the same colour of the friction pen.
A piece of paper or any surface where you want to perform the trick.
A heat source, such as a hairdryer.
Procedure:
To prepare the trick write a message with a normal pen. Hide this message using a friction pen. For example write random letters between the letters of the message. This way what is written is imperceptible to the public.
Ask someone in the audience to say the magic words: "For the words to show, heat must bestow."
As the heat is applied to the ink marks, they will "magically" disappear right before the audience's eyes!
Frixion pens contain thermochromic ink which vanishes when the heat from the friction of erasing is used to make the ink disappear. This can be used to reveal secret messages as shown in the video, by using heat to make the thermochromic ink disappear and leave visible writing done in ink from a normal pen.
Note: There are many brands of pens with thermochromic ink, in the following link you can find some.