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Hello, around 5,000 years ago the Egyptians were using glass to make beads, melting

sand at very high temperatures and cooling it rapidly in water. Ever since glass has been

deeply puzzling, scientific advances reinforce the urge to understand

the glass from spectacles, prisms and telescopes to optical fibers and the windows on space

rockets to mobile phone screens today. How can it be made stronger or clearer and what

does it do to light? Many glassmakers have kept their methods secret. In Venice

in the Middle Ages, disclosure was punishable by death. Scientists still don't precisely understand

what happens when sand moves from a molten state to a hard transparent phase, when

it appears to have solid and liquid properties. With me to discuss Glass, one of the great scientific puzzles, are Dame Athena Donald, Professor

of Experimental Physics at the University of Cambridge and Master of Churchill College Cambridge,

Jim Bennett, former Director of the Museum of the

History of Science at the University of Oxford and Keeper Emeritus of the Science Museum,

and Paul McMillan, Professor of Chemistry at University College of London.

I think you don't know, glass starts us something solid, mostly sand, then it's molten and once

cool it's a very different solid. What do we need to know about the different states of

matter in that process? The three familiar states of matter are gases, liquids and

solids, and if we think of something like water with which everyone's familiar in each of the three states,

it's quite easy to describe what's going on. So in a gas, the atoms or molecules are far apart.

They're moving very fast. You cool down into the liquid phase,

the molecules of water in this case would get much closer together, their movement is much

...