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How do chemical ink erasers work? Do they actually erase the ink?

Posted November 28, 2019

Do you remember that myth that the blue end of the eraser is for ink? Of course, that wasn’t true, but ink erasers do exist. In fact, you’ve probably seen them many times – schoolchildren use them quite often. But how do they work? Do they actually remove the ink?

The problem of removing ink from paper always was very important. Admittedly, this question was even more important back when computers or even typewriters didn’t exist. Back then people used special ink erasers – tiny little metal scrapers that allowed removing the ink together with the top layer of the paper. We should be grateful that we didn’t need to fix our errors using such meticulous processes.

A modern ink eraser – no more metal scrapers. Image credit: Guillaume Piolle via Wikimedia (CC BY-SA 3.0)

But let’s go back to those chemical ink erasers. They are marker-like tools, filled with clear liquid, smell of which you remember very well (although you shouldn’t sniff it too much). That liquid is actually what the eraser is. It was invented back in 1930’s by the German manufacturer Pelikan. It took them some years to put it into production in a consumer-friendly form factor. Ink eraser, known as Tintentiger back in the day, came onto shelves in 1972.

It works great with royal blue ink. You just have to pass the eraser over the text and see it disappear in front of your eyes. It almost looks magic. However, it is not that magic – the ink actually does not completely disappear and can be returned using aldehydes. Essentially, ink erasers just make ink invisible, without actually removing it. But how?

Ink erasers do not actually erase the ink – just make it invisible. Image credit: Guillaume Piolle via Wikimedia (CC BY-SA 3.0)

Well, all objects have their colour just because they reflect a certain portion of the visible light. Blue ink has tiny little crystals that reflect blue. An ink eraser has sulfite or hydroxide ions that bind to the central carbon atoms of the dye. This changes the internal geometry of the ink, shifting its pigment and making it transparent (or nearly transparent). Once the eraser is dry, you can write in that place using a different pen.

And that’s the think – ink erasers typically work only with royal blue coloured ink. It will turn black into rust brown and other shades of blue will still be visible. Some special ink erasers are developed for those different inks, but only the original is so effective with its blue ink.

People want to remove ink because they made a mistake, but nowadays we rarely use our handwriting and an royal blue ink. If you are writing something by hand, it is likely a postcard or a letter. If you made a mistake, start over – ink eraser may leave a spot or may not allow you to write something else in the same spot.

It is funny how we take these things for granted. Ink erasers cost pennies now, but they are an ingenious piece of tech.

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