Breakthrough: The Ideas That Changed the World

(sweeping orchestral music) In the 13th century, Venice is the world center of glass-making. And most of the innovation which takes place here is to be found on this small Venetian island called Mirano. The fierce competition of glass-makers here meant that it's a kind of geek's paradise for glass. It was the very first time people cared about every single technical detail to create the most beautiful work that they possibly could. Most glass at this time is opaque due to bubbles and impurities in the mixture. The holy grail for the artisans in Mirano is to work out how to make glass perfectly clear, through careful and meticulous experimentation with new and old ingredients. On the trade routes between east and west, Venice could easily source the main ingredients of glass. Silicon dioxide, or sand, and various sodium and calcium mineral salts. The secret was the shift from the use of mineral salts to plant-based salts, from plants which grow in salty environments, and a particular plant that we call samphire, which traps salt, but almost nothing else, and so when you burn it you get a very clean, pure material to add to your silica to create your glass. Remarkably, the ash from this marine plant significantly reduces the melting point of silica. Which allowed them to keep it at a temperature where the glass was liquid enough that any little bubbles or impurities would come to the top and pop. This, then, was the revolution which would allow them to make glass which was very clear and very pure. And it was that shift which allowed the Venetians to create this very, very transparent cristallo, the name given to clear rock crystal by the Greeks. (energetic music) -

Narrator

This was the first time we had mass-produced clear glass. This revolution in glass technology would have many consequences for society, but perhaps the greatest was the way it would change how we saw the world. Here in the basilica of San Nicolo in Treviso, just north of Venice, lies evidence of what must have seemed an astonishing invention at the time. Painted by Tommasa da Modena in 1352, the fresco depicts a group of monks in a monastery scriptorium, poring over their manuscripts. But look closer. One of them is wearing spectacles. This exquisite fresco from almost 700 years ago is the first image of spectacles in society. It allowed the monks to keep on reading and writing for decades longer than before. They didn't have to accept failing eyesight as the will of God. They didn't have to delegate the really important task of acquiring knowledge to younger people. They could just keep on going, and so they did. We don't know who created these first glass lenses. They are lost to history. But it's no exaggeration to say that you can draw a direct line from these spectacles to the extraordinary optical instruments that we use today to gaze into space.