Erasable Pens - How Do They Work?

Around here at Honest Paper, we love our Legami Erasable Pens; with their veritable menagerie of animal themes and colours, they’re sure to put a smile on the face of any stationery lover! But we got to thinking - what makes these pens tick? How can ink be erasable?

Our hypothesis was that the heat from the friction of the eraser was what erased the ink. Seems obvious. But to test this heat theory, we wrote some things down in a notebook and left it in a  hot car for a few days. Lo and behold, once we retrieved the notebook, we saw that the writing was indeed gone. 

That wasn’t enough for us though, we wondered, if heat alone can erase the ink, can it be returned by low temperatures?

Why, yes it can; we subjected the notebook to the cold embrace of a freezer and after a little while, the writing had reappeared like magic!

So the ink doesn’t really erase, what’s at play here - is it truly sorcery or something else?

Well, the mechanism of erasure depends on the kind of ink the pen uses. Back in the day, erasable pens used a kind of rubber cement, which acted like a liquid when the pressure of writing was applied. It could be removed immediately after writing, but after a few hours it would harden and become permanent.

Since the late nineties most erasable pens use what’s called ‘thermochromic’ ink. This special ink uses a fancy, little bit of chemistry to make it seem like the ink has been erased. The pigment contains something called Leuco dye, which, when it is chemically bonded to certain molecules, has colour and looks like regular ink. But when it is heated above a certain temperature (usually around 60°C), it reacts with a special, temperature sensitive compound, which breaks the bonds, rendering the dye invisible to the naked eye. And as you might expect, when you make it really cold, the bonds can reform, bringing its colour back into the world!

So, there you go - a little bit of the science that goes into erasable pens! While, they’re cool and useful for everyday writing, but just remember never to write or sign any important documents with them. You may find that your signature comes and goes with the seasons…

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Written by our awesome team member Luke :) 

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