It was first invented in the 1970s. They’re still working on it today.

What if any surface could be digitally changed to show whatever pattern or image you wanted? If you could change your room’s wallpaper as easily as you change the wallpaper of your desktop?

Okay, that may be a bit of an overkill for most people. But it would be useful for interior designers, who could then change the look of the room with a tap of the screen, trying out different layouts without having to actually change anything.

Other people may be more interested in road signs that automatically update when needed, billboards that can be changed without having to use up blankets of paper, or just a low-power indicator on the outside of you hard-disk so you can tell, at a glance, how much space is left.

The beauty of these surfaces is the fact that they don’t use up electricity, as normal digital screens would do. They only need power to change their display; once changed that’s how they remain.

But when you first hear the words “electronic paper”, you don’t associate it with any of those things. First, you’d associate it with reading books. Or rather, e-books, which, depending on your view, is not at all the same thing.

I once asked my friend if he had got any new books to read. His response: “You mean…‘book’ books?”

Newspaper and magazine sales are going down across the world. Publishers are struggling to keep their funds coming. Bookstores are seeing less customers too, and libraries are either scaling down, adapting for the future, or closing altogether.

That’s because, in recent years, more and more people have gotten into the habit of reading things digitally. People are switching from tabloids to tablets, and preferring PDFs over paperbacks. They’re moving, slowly but surely, from simple sheets to scrolling screens.

And with that change in reading habits has come a new device: the ebook-reader, or ‘ereader’ for short.

Actually, ebook readers are not all that recent. The first commercially available one was launched in 1997. That was the Rocket eBook, created by Martin Eberhard and Marc Tarpenning — the same people who later went on to start the electric-car company Tesla Motors (which is no longer just a “car company”).

The Rocket eBook used an LCD screen, similar to the ones in calculators, Nokia phones, and old videogames, but with a sharper resolution. It was quite successfull, selling 20,000 copies in the first two years — and it had a few competitors as well! But it was quite expensive, at $400 apiece, and many people didn’t really see the point.

Nowadays, when people say “ereader”, they don’t think of the kind of screen the Rocket eBook had. When you say the word, you think of a completely different screen technology: E-ink.

Actually, E-ink is just a brand name for what is called “electronic paper”, or “e-paper” for short. Two things set it apart from other digital screens: it doesn’t use electricity except for changing the screen, and it uses natural reflected light that eyes are most accustomed to.

The first e-paper device was the Sony Librie, which came out in 2004. It was followed by the Sony Reader. Soon, other companies like Alatuarek and Infibeam started making their own models too.

This time, e-readers were actually becoming popular. They were easy on the eyes, because they used natural light, and didn’t shine their own bright flickering light straight into your eyes. They were easy on the batteries, because they didn’t guzzle power simply to keep the screen on. And they were easy on the backpack, because they could hold hundreds of books in one small case.

In the days of BlackBerries and PalmBooks, all these features together answered the question: Why should I buy a new device just to read a book?

The ebook-reader market, though small, was fast expanding. More and more people were getting interested. When Amazon, the world’s largest book seller, brought out the Kindle, e-paper was widely touted as the future of reading.

But then came the iPhone and iPad; the smartphones and tablets. People now had a different question to be answered: Why should I buy a device just to read books, when I can get a device that lets me read books and do so many other things as well?

Electronic paper has been in development for a long time. They idea first came up at a Xerox lab in the 1970s, along with ethernet, laser printers, graphical desktops, and the computer mouse.

Incidentally, the main reason for making e-paper was not that other screens were too bright, but that they were too dim.

The computers at the Xerox Palo Alto Research Centre (Xerox PARC) had very dim screens. If people wanted to use them, they had to do it in a dark room, with the windows darkened and the lights switched off. Perhaps that was why they didn’t really appreciate what they were using: the world’s first personal computer.

Until that time, all computers were huge, networked mainframes. Many people would sit and work at “terminals” — sets of big, bulky screen and keyboard — which all connected back to the giant computer in the middle.

Things were now changing. Xerox had recently invented the graphical interface and the “mouse”, a device that let you point and click on things instead of having to learn the keyboard. And now, with the Xerox Alto, they hoped to present a new kind of computer: one that could be used not at the office, but at home.

The problem was, it would have to be a very dark home.

The Alto computer used the very best technology available at the time. Even that was too dim. If people wanted to read something more then a few pages long, they would always print it out on paper — only to send it to the dustbin by the next day.

That’s why, in 1974, PARC employee Nicholas K. Sheridon created a whole new kind of screen. That was Gyricon, the world’s first electronic paper.

How does e-paper work? It’s taken many years to get the details right, but the basic idea is quite simple.

It works like a Magna Doodle.

You know, that erasable magnetic toy slate? The plastic thing you can draw on with a metal pen, or stamp patterns on with magnets? Whose screen is cleared by running a long bar-magnet across the other side?

Yes, that’s the one I mean.

The Magna Doodle works like this: it’s divided into many hexagonal cells — just like pixels, but you don’t have to try very hard to see them. Inside each cell is some metal dust, like iron fillings, which gets attracted to magnets.

So when you put a magnet (or the pen, which is also magnetic) above a cell, all the iron fillings in that cell get attracted and rush to the top. The top of the hexagon is semi-transparent, so you can see the black iron below.

The “eraser” is also a magnet. But it’s on the opposite side of the screen. So when you run it across, all the iron fillings go to the back, leaving the front side an empty white.

When I was young, my Magna Doodle broke. The screen came detached from the plastic frame. That’s when I made a discovery: if I draw something on the screen, it comes to the opposite side too — but in inverted colours!

While the main picture is black on a white background, the back of the screen showed up as white on a black background. That’s because the “black” never went away: it was just travelling from one side to the other.

‘Gyricon’ is Greek for “rotating picture”— icon as in ‘image’, and gyre as in “did gyre and gimble in the wabe”.

The Gyricon screen worked in a similar way to the Magna Doodle. But there were some differences. Instead of iron fillings in hexagons, it had many small plastic beads. Each bead was painted black on one side and white on the other, and had a tiny, round magnet inside. The beads were suspended in a kind of oil, so they could turn smoothly.

And there was another difference: instead of being controlled by a pen on top, it was controlled by electrodes at the bottom.

Electrodes are tiny things that can be set to have either a ‘+’ or a ‘-’ charge. That charge can be changed electronically, to make the beads turn to the correct direction. Depending on the picture, either their black side or their white side can face upwards. And then, the electricity can be switched off: the beads stay right-side-up on their own.

Nick Sheridon was working on Gyricon for a while to make it better. But then, Xerox told him “We’re not in the screen business”. They asked him to work on a new ink for printers, to keep up with the Japanese competitors that were coming in.

(That new ink worked, and the company became so successful that “xerox” is now used as another word for “photocopy”).

Meanwhile, researchers at MIT Media Lab had made a new kind of e-paper. They called it an “electrophoretic display”.

The new screen wasn’t divided into beads or hexagons. It had tiny white particles of “titanium”, floating in a black liquid. Meanwhile, the screen-dividing happened in two layers of electrodes — one at the top, one at the bottom. The top layer of electrodes is transparent, so you can see right through it. And both layers work together to attract the titanium to the right side of the screen.

(Some kind of electric charge has to be added to the liquid, to make the titanium magnetically charged. Otherwise, it’ll get attracted to both ‘+’ and ‘-’ electrodes, which isn’t very helpful at all.)

The MIT group later went on to start their own company, now known as the E-Ink Corporation.

E-paper is far from being the default screen of choice. There are two main problems to be solved. One is the screen refresh rate: it takes much longer than other displays to change what’s on the screen. The other problem is that most e-paper is black and white. You can’t see things in colour.

The second issue is being worked on. People are using new techniques, involving oil bags and coloured, charged liquids, to make coloured e-paper. At the moment, it takes two whole seconds for a colour screen to change — much too long for a tablet or ereader. But that’s not what it’s being used for. Instead, it’s being marketed for auto-changing billboards, as well as for artists and designers to try out new scenes.

Ordinary, black-and-white e-paper is used for many tiny things, from price-tags in shops, to digital watches, to smart usage-indicators on your hard-disk.

And then, there’s work on to make e-paper more flexible. Until now, most e-paper screens have been less like paper and more like a thin, brittle cardboard: you can write on them, but can’t bend them. But now, people are trying to use flexible plastic sheets and graphene, to make the screens more bendy. If the succeed, e-paper will really be almost like paper.

People still use their tablets and smartphones to do their reading. Screen technology has progressed, and the flicker-problem has gone. Modern LED screens now refresh their lights so fast, your eyes don’t even notice it. Their resolutions are higher too, letting you see things more sharply.

Some people still use e-paper for their reading. They don’t want the bright light, or the mirror-like reflections that most screens give. They like the fact that it can be used in bright light without having to make the screen bright as well. Or, maybe they just want the longer battery-life.

Night-time reading is a different matter. The bright light from tablet screens could disrupt your sleep-cycle — not to mention the social media notifications, who can probably handle the job on their own.

An ereader, on the other hand, is a bit low on contrast. All the new models come with an in-built ‘frontlight’ to light the screen, but the pictures are still a bit greyish and not as clear as paper. And then, there’s the question of where to keep it when you’re done, so you don’t sleep on it by mistake.

Maybe it’s time to switch back to a good old ‘book’ book?

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