Hey Ray: Erasable pens and reappearing images
PITTSBURGH (KDKA) -- Some things are very sensitive when it comes to temperatures, and we are going to do an experiment that uses a temperature sensitive ink. "Temperature sensitivity" means that the inks behavior is dependent on the temperature.
This temperature sensitive ink is easily found in stores, as it comes from a special type of erasable pen. Just like other erasable pens, when you make a mistake, you can erase it. This is a newer type of erasable ink, though.
When you rub the eraser on it, the friction from the eraser rubbing on the paper generates heat. The heat is what makes this newer ink disappear. You may have even seen people on social media making messages disappear with a hair dryer or other heat source.
While the ink seems to disappear, it is really still there! That is what makes this newer kind of erasable ink so cool.
The ink pen we're using here, manufactured by Pilot, turns transparent after it is heated to 140 degrees or greater. That means you don't need an eraser. You just need to add heat to make it disappear. The disappearing act isn't temperature sensitive ink's only trick, though.
This means we can make it reappear.
While heat makes the ink seem to vanish, cold will make the ink reappear. Whatever seemed to be erased from the paper in there long enough, the messages will reappear.
According to Pilot, the maker of the pen, this ink contains special microcapsules which hold the color. The contents of these microcapsules are what react to the extreme changes in temperatures.
Just like water reacts to extremes in temperatures - like freezing at 32 degrees and boiling at 212 degrees - the contents in the capsules have different color properties based on temperature.
Leuco dyes behave this way. They are a special kind of dye that can switch between two different chemical forms. One that is colorless and one that has color. Some of these dyes are temperature sensitive and others are dependent on the presence of acids or bases, like the disappearing ink experiment we did.
