Invisible Ink Pen
This is cool. It writes like a normal pen, but if you run a hair dryer over the written words they disappear. And if you put the paper in the freezer the words reappear. Fantastic.
EDITED TO ADD (5/20): This is the same technology as the widely available Pilot Frixion pen. Here’s a temperature sensitivity test, and a freezer test.
SeanN • May 19, 2009 7:39 AM
Useful, unless you live in the Sahara or North pole where the climate may give the game away….
Si