There’s a lot of ancient writing that  we know about but just… don’t have.

People go wild thinking about what could be  hidden in the lost writings of, say, Aristotle But writing is fragile, and  texts can easily disappear. Not because of one specific  library burning down necessarily.

Rather, texts have been lost, damaged,   or even intentionally destroyed by people  who wanted to reuse their materials. But sometimes, a text is not  quite as lost as it seems. Modern technology offers us  some amazing ways to recover   writing that seemed like it was lost for  good, in those damaged and reused pages.

It’s as if we’ve just started finding the keys  to a bunch of centuries-old time capsules. And now, historians can start recreating a  library of texts that give us a fascinating   look into the past, at some of the  foundations of our modern world. [♪ INTRO] In 1947, some Bedouin shepherds wandered into a cave on the northwest shore of the  Dead Sea, looking for a lost goat. Instead, they found 11 ancient jars.

And one of them held three long-lost scrolls. Once word got out, archaeologists rushed  to the scene and spent the next nine   years scouring nearby caves, where they dug up  thousands of pieces of falling-apart scrolls. Carbon dating revealed that they  were two thousand years old.

The scrolls were in rough shape. Many were just lying on the floor,  getting ruined by water and the elements. Others had gotten buried in bat  poop or partly turned to liquid.

But amazingly, some of these ancient texts  were salvageable — with the help of science. The key to decoding these scrolls actually  came from a NASA scientist whose lab used   a technique called multispectral  imaging as a way to explore planets. Multispectral imaging involves  capturing the same photograph   multiple times, but at different wavelengths.

Normally, when you take a  picture with a regular camera, you’re capturing the full range of  visible light, from violet to red. But when you take a picture  using multispectral imaging, you only capture one narrow  range of light at a time. So, one image might just capture violet  light, while another only detects red light.

You can also capture wavelengths  that aren’t visible to our eyes,   like ultraviolet and infrared. The key is, different objects  reflect different wavelengths   of light depending on what they’re made of. So, once you see what wavelengths  an object is reflecting,   you can often figure out what it’s made of.

NASA scientists use this technique  to figure out what types of surfaces   are reflecting light into their cameras. And one of them realized this technique might just  be the key to decoding damaged documents as well. See, when you’re dealing  with an old, damaged text, it can be hard or impossible to read the faded  words, especially if the surface is stained.

But, even if the text is faded,   it may reflect some light at certain  wavelengths where parchment does not. So multispectral imaging can help improve the  contrast between the text and the surface it’s on. It can also help where there  are stains covering the ink.

To your eye, it might be impossible to  make out a letter against a brown stain, because your eye is seeing the full  spectrum of wavelengths at once. But if you have a camera image  specific wavelengths at a time, the ink may stand out in some of those photos. And scientists did this with some  fragments of the Dead Sea Scrolls, and suddenly, invisible words came into focus.

They were written in various languages,  including Hebrew, Greek, and Aramaic. In case you haven’t guessed it, these  Dead Sea Scrolls turned out to be the   oldest Biblical manuscripts still in existence. They were over a thousand years  older than the oldest-known   copies of the Hebrew Bible, aka the Old Testament.

Reviving these texts has kept  scholars busy for decades. They’re still at work filling in  details of the region’s history   and exploring how the ancient religious traditions   captured in these texts grew into world  religions like Judaism and Christianity. A little bit further west,   around the same time that scribes in the  Levant were writing out these scrolls, Ancient Greek scientists and philosophers   were writing out all sorts of  treatises on the natural world.

Time has done away with many of those  too, but now and then, we get lucky. In 1906, an interesting old prayer book  turned up in a library in what’s now Istanbul. It was full of Christian prayers  written in Greek in the 13th century.

But the interesting part was a  shadowy text underneath all that. Back in the day, old works written on  parchment were often erased and written over,   because parchment was sometimes more  valuable than what was written on it,   at least in the opinion of the scribe at the time. That produced manuscripts with multiple layers of  text written over each other, called palimpsests.

In this book, the second, faded  layer of text hidden under the   lines of prayer was also written in  Greek, mixed with symbols and math. It wasn’t all legible, but a Danish scholar  managed to piece together some of the text   and figure out that he was looking at copies  of seven treatises written by Archimedes. Archimedes was a legendary Greek mathematician  who lived in the third century B.

C. E. He’s known for discovering pi  and the foundations of calculus… He also supposedly invented a screw  pump to lift water against gravity.

Unfortunately, a lot of his work has been lost  in the over two millennia between then and now,   but the work that has survived can give us a look   at what amazing science was  happening during his time. And two of the seven treatises uncovered in  this prayer book were completely unknown! So this was a really exciting discovery.

Except, just two years after this palimpsest  was discovered, the book vanished. It was gone for almost a century… until it resurfaced at a New York auction in 1998. The guy who eventually shelled out $2 million  for it then lent the book to a museum.

It was now in even worse condition. Pages were missing, and mold was  covering some of the surviving pages. But scientists could now examine it with modern  technology and piece together more of the text.

As with the Dead Sea Scrolls, they  started off with multispectral imaging. This can be a good tool for uncovering  the faint undertext in palimpsests, because it can bring out the contrast  between the text and the parchment. But that’s not always the case.

These copies of Archimedes treatises were  written by different people with different ink, and some inks just never  popped out against the paper. Because if one ink responds to different  wavelengths the same way as the parchment, you’re basically looking  for a black cat at midnight:   There’s no contrast to set  one apart from the other. And that’s what happened with  part of the Archimedes Palimpsest.

Scientists just couldn’t see the text. So they went with a different approach. They tried to bring out the invisible  text using ultraviolet fluorescence.

Fluorescence is what happens when you shine a  light on something and it glows in response. Certain materials do this in response  to UV light, including parchment. It gives off a bluish glow.

So when scientists put the  manuscript under a UV light,   the parts that were covered with ink — including  the hidden text — stood out against this glow. That left scientists with an image that captured  both the newer text and Archimedes’ text. Now they were close.

To get Archimedes’ text alone, they subtracted  a regular image showing just the newer text. And finally they had the hidden text before them. It took a few more analytical tricks  to make the text fully legible,   but the manuscript’s UV fluorescence was the key.

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Now, not every material fluoresces, and the  ones that do fluoresce do so in different ways. Some glow in response to UV rays,  others in response to X-rays. And the glow they give off is different too.

This makes fluorescence a really  useful trick for deciphering old texts. We just saw an example of  fluorescence under a UV beam,   but if you shine a beam of X-rays onto  some parchment, you’ll find that this   time it’s not the parchment that glows,  but, if you’re lucky, the ink itself. And scientists used this trick to rescue   one of the most intriguing lost  texts they’ve ever come across.

This one showed up in an old  book bound in the 16th century. The book itself was nothing special, but on  its back cover, some black paint had worn off. Underneath was a hidden text.

It wasn’t a total surprise, because bookbinders   from this era often recycled materials  from older books to bind new ones. On one hand, that was a pretty tragic  decision – from our point of view – that   led to the destruction of countless old texts. But on the other hand, it ended up  preserving a bunch of texts that   might have just fallen into oblivion otherwise.

So today, we have a bunch of old books  full of stowaways from even older times. This particular text was completely  impossible to read with the naked eye, but this is where scientists  turned to fluorescence again   in an attempt to see through the paint. This time they used what’s known  as macro X-ray fluorescence.

Essentially, they used a scanner to  shine an X-ray beam onto a surface. The ink fluoresced in response… and ultimately  revealed not just one text, but three! Each one had been written in a different  kind of ink, with different metals in it.

The most recent one was around the same age as  the book itself, and had been written in cursive. It showed up thanks to the glow of iron  that had been in this scribe’s ink. Underneath that, the glow of mercury revealed   another script from the 14th century  that seemed to be written in red ink.

And underneath that was the real prize: Traces  of calcium revealed a text written in the 12th   century that quoted a passage from an English  scholar named Bede, who lived in the 8th century. Bede was basically a walking encyclopedia. He wrote a ton about the history of England,   he wrote scientific manuals, and he  wrote interpretations of the Bible.

We owe a lot of what we know  about medieval England to Bede. The text buried in the back cover  of this book was not unknown,   but the discovery was still a big deal. It showed historians where his work was   circulating and who might  have been influenced by it.

And that helps us understand how knowledge spread   among people and places at  different moments in time. Rescuing old texts like this can bring to  life whole worlds that we’ll never know. But some texts weren’t just scraped off  or sliced up to make way for new work.

In Mesoamerica, conquistadors who arrived in the   16th century systematically burned all  the indigenous works they could find. Today, there are just over a dozen known  manuscripts remaining from pre-colonial times. One of those is the Codex Añute.

It’s a document produced by the Mixtec culture,  and comes from the area that’s now Oaxaca. Unlike the manuscripts from  Europe and the Middle East,   this one is made up of colorful  pictographs drawn on strips of leather. The leather was folded up like an accordion and   covered with a chalk mixture,  to create stiff, white pages.

In the 1950s, one researcher was studying  this document when he noticed what looked   like hidden images peeking out  through cracks in the surface. As far as he could tell, it looked  like he had a palimpsest on his hands. But it wasn’t until decades later that  scientists had any luck viewing those images.

This palimpsest was especially tricky because  the paints used on this document were organic. They didn’t contain metals  like the other inks we’ve seen. That made all those tricks for detecting  traces of metals completely useless here.

But in a study published in 2016,   researchers revisited this document using  a technique known as hyperspectral imaging. This method is similar to multispectral imaging. With multispectral imaging, you’re capturing  images at a few different wavelengths.

But with hyperspectral imaging,   you capture hundreds of images from all  the wavelengths across the whole range. You end up with a whole bunch of data,   so it takes special software and some serious  computer power to crunch through it all. It’s not going to be the go-to  method for every hidden text.

But the benefit is that it brings out  really nuanced color variations that are   too subtle for us to pick out with our eyes…  or even with regular multispectral imaging. In this case, researchers were able to  uncover hidden pictographs representing an   account of the ancestors of the codex’s  authors, going back for generations. Scientists haven’t been able to  fully interpret the pictographs yet,   and there are some parts that  they still need to uncover.

But they hope that eventually they can use  the recovered images to better understand the   way of life of the people who made them and  the archaeological remains they left behind. Given how few of these codexes we have,  getting two for the price of one is huge! Many of these technologies are new, or only  recently being used to explore lost texts.

But as researchers put them into practice, little  by little, it’s like they’re opening an invisible   door to a library full of ideas and history that’s  been there all along, just waiting to be unlocked. [♪ OUTRO]