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This is the vibrant heart
of a 21st century city.

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There's something strange but
wonderful about Piccadilly Circus.

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Strange because,
as far as the eye can see,

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there's nothing natural.

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There's not a tree, not a flower,
not a blade of grass.

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But wonderful because we made it.

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We've transformed matter
to create the world that we live in.

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My name is Mark Miodownik,
and as a materials scientist

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I've spent my life
trying to understand

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what's hidden
deep beneath the surface

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of everything
that makes up our modern world.

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For me, the story of how materials
have driven human civilisation

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from the Stone Age
to the Silicon Age

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is the most exciting story
in science.

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Without our mastery of the stuff
that we found around us,

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we would have no buildings, no cars,

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no roads, no art.

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Nothing.

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This series is the story of how
we created our 21st century world,

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how we unlocked the secrets
of the raw materials of our planet

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and created our future.

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Gleaming, lustrous, volatile metals.

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Everything around us
is shaped by metal.

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Metal has driven human civilisation
- power, war, industry -

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and yet it's mysterious stuff.

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It's only in the last 60 years
that we've begun to unravel

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the secrets hidden deep within
the metal at the atomic scale,

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how it is that it can be
strong enough to build empires

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and yet soft enough
that I can crumple it in my hand,

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why it is
that it seems inert and unchanging

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and yet sometimes can behave
almost as if it's alive.

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Take a look at this.
It looks like a normal paperclip,

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but if I scrunch it up
so it's unrecognisable

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and then put a blowtorch on it...

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HE LAUGHS

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Isn't that amazing?
Isn't that marvellous?

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I mean, that is indistinguishable
from magic.

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This...
This metal remembers its shape.

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Normal metals don't do this.

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We've engineered this metal
to have a memory.

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How we got from the Stone Age
to being able to manipulate matter

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and make metals like this
is the story of this programme.

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Let me take you back
to when it all began -

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the dawn of civilisation.

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This is where our ancestors
first settled.

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It's where East meets West,
where Africa meets Asia.

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Underneath my feet,
the Earth's crust is shifting.

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And the geology here
gave our ancestors

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access to something
that would change their world.

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This is one of
the first places on Earth

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that man stepped out
of the Stone Age

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and transformed rock into metal.

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And it all started with copper.

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It's these green streaks
that may have been the first clue

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there was something
a bit special about this rock.

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Somehow, we worked out that
when you've got this type of rock,

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you can do something amazing
with it.

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We don't really know
when our ancestors first discovered

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what this marvellous
green rock can do.

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They might have just ground it up

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to use it as a powder
to decorate their pottery,

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or maybe it happened to be
just lying by the fire.

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But either way, they discovered
something really rather marvellous

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about what this stuff can do
if you add it to a fire.

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Now, the thing about the fire is,
you need it to be very, very hot

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and for that you need a lot of air,

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and that's why they built
their fires on hillsides.

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These hillsides are extremely windy,

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so the air is being funnelled
into the fire.

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It's actually a genius idea.

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And then,
when they'd got a very hot fire,

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they added the green rock.

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And then they kept the temperature
high for hours, and they waited.

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So when the fire died down,

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they would have found bits
of a hard stone, black stone,

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but amongst that black stone,

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look, there's tiny little
shiny bits of metal.

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They'd transformed rock into metal,
it's absolutely extraordinary!

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Here we have rock...
I mean, there's rock everywhere,

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but they'd found
the power of transformation.

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Look! Look how bright that is!
A bright piece of copper.

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We know they did it on this hillside
because we've found the remnants

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from early smelting
of our ancestors.

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So they did that here,

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and this was the beginning
of human civilisation,

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the age of metals.

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Our ancestors realised that
with copper,

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they could make strong tools,

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better than anything
they'd had before.

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This copper chisel represents
the leap out of the Stone Age.

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Everything we have
in our civilisation today

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is due to metal tools like this.

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If they get blunt,
we can sharpen them.

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If they get bent,
we can re-straighten them.

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If they get damaged,
we can repair them.

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It's simply
the perfect material for tools.

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Nothing else
our ancestors had in their world

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could have done this -
not stone, not bone, not wood.

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So what's so special about metal?

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It's all down
to its inner structure.

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Metals are made of crystals,
and that's a very surprising fact,

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because they don't seem to behave

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anything like the crystals
we are more familiar with.

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I'll show you what I mean.
I've got a quartz crystal here.

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That's what you mean
when you say "crystal".

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And this is what a quartz crystal
says when you hit it with a hammer.

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You see? That's what we think of

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when we think of crystals being hit
with a hammer.

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But if I say to you that this piece
of metal is made of crystals,

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you know already
that it's not going to do that.

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It's going to be quite malleable,
I can do this.

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In fact, that's how you work metal,
you change its shape.

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And that's...that's really strange,
because that means

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that the crystals in this metal are
changing shape instead of exploding.

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Inside the metal crystal,

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the basic building blocks of
everything in the universe, atoms,

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are arranged
in a regular lattice structure.

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But they're not static.

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When they're hit, metals can shuffle
atoms from one side to the other,

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like a Mexican wave.

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They can move, rearrange themselves,

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and this is why
the crystal can change shape.

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Metals alone behave like this.

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As well as not shattering
when you hit them,

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they actually get stronger.

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The impact creates waves
of shuffling atoms

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which collide with each other
and create blockages.

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These make it harder
for the atoms to shuffle around,

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making the metal stronger.

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So the more hammering you do,

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the more blockages you form
in the crystal,

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and so the stronger the metal gets.

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It was the strength of metal
over stone and wood

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that became its main attraction.

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With metal tools,

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our ancestors could conceive
of grandiose projects.

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It's believed the limestone blocks
that built the pyramids of Egypt

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were carved using copper chisels.

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But soon copper wasn't enough.

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Our love affair with metals
consumed us.

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Here on the shores
of what's now Israel,

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metals from distant lands
were traded.

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And it was one of these, tin,
that moved on the story of metals,

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as our ancestors
began to mix metals together.

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So they took some copper...some tin,

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and they melted them together
to make a mixture,

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which we call an alloy.

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And they created a new metal,
bronze.

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Bronze was the creation
of man the metal-smith,

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rather than a gift of nature,

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and it gave its name to a new era,
the Bronze Age.

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Now, this is a nail
made out of pure copper,

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and as metals go,
copper's pretty weak.

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Have a look at this.

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After a while,
it just can't get any further,

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and so the metal itself buckles.

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If I do the same with tin nail...
let's see what happens.

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Tin is actually softer
than copper, even.

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That's a real joke for a nail,
isn't it?

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But here's the odd thing.

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The mixture, a bronze nail...

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well, this is much stronger.

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Ha-ha-ha-ha!

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It's so strong it's knocking
the wood out of this vice.

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So that's odd, isn't it?
You add two soft metals together,

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and you get something much harder
and much stronger.

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How do you explain that?

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In bronze, the tin atoms
replace some of the copper atoms,

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which are smaller.

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This interferes
with the lattice structure,

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making it more difficult for the
atoms to shuffle across the crystal.

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This makes the new alloy
much stronger.

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The strength of bronze

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gave us the means not only to build,
but to destroy.

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As well as tools,

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we made the swords and shields
of conquest and dominion.

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Bronze propelled the evolution

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of a new, complex,
more technological society.

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It also created new occupations,

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such as mining, manufacturing
and trading metals.

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Bronze dominated the world
for 2,000 years.

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But it wasn't the metal
to take us into the industrial age.

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About 1200 BC,
another metal rose to prominence.

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Iron.

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Iron is one of the most plentiful
elements in the Earth's crust,

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but it's fiendishly difficult
to work with.

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Owen Bush has spent nearly 20 years
learning how to tame iron.

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It doesn't look very promising

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as a way to start a civilisation,
does it?

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It's the basics, the beginning of it.
So what happens next?

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You take this stuff... Heat it up.
OK. And hit it.

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Pure iron can't be easily extracted
from its native rock.

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There are several stages before
it can be hammered into submission.

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So this whole process of bashing it

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and putting it back in the furnace
is to get purer and purer iron.

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Yes, it is. You're trying to purify

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this very strange substance
that's come out of the furnace.

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Yeah, I'm literally
beating the crap out of it.

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As Owen continues
to hammer the iron,

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more and more impurities are exposed
to the air and burn off as sparks.

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By bashing it,
you're left with a purer metal.

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This is wrought iron,

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wrought at the blacksmith's anvil.

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If you'd like to have a bash,
by all means.

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00:13:34,580 --> 00:13:37,380
I would love to do that,
I've never done that before.

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00:13:37,380 --> 00:13:42,700
Mastery of iron by our ancestors
would not have been easy.

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00:13:42,700 --> 00:13:46,220
To show me just how difficult it is
to work with, Owen challenges me

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to make the simplest and most common
of iron products.

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Well, we're going to try and squash
it flat and forge a nail out of it.

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I know in theory
what this stuff should do,

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00:13:56,660 --> 00:14:00,700
but I've never hit it with a hammer,
I've never done what you do.

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00:14:00,700 --> 00:14:02,140
That's good to go. OK.

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00:14:02,140 --> 00:14:03,540
Right.

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00:14:05,500 --> 00:14:09,140
That's it. Oh, yeah, so there's bits
flying off, I can really feel...

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00:14:09,140 --> 00:14:11,460
You can feel something happening
in the metal.

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00:14:11,460 --> 00:14:13,940
There's a kind of response to you.

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00:14:13,940 --> 00:14:17,980
There's something addictive to this.
Yeah, it's primal, isn't it? Yeah!

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00:14:17,980 --> 00:14:20,700
Now, yeah, back in. Back in, yeah.

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00:14:20,700 --> 00:14:23,260
You can see, when it came out,
it was bubbling,

220
00:14:23,260 --> 00:14:24,860
and as it cools down the...

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Yeah, then I can see it
becoming a bit brittle.

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It sort of freezes in your hands
and you're not making any headway.

223
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Yeah, well,
you're getting feedback from it,

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and because every bit's different,
you have to use that feedback

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so you don't end up with a flattened,
destroyed blob, fundamentally.

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00:14:50,460 --> 00:14:52,540
What I began to learn with Owen

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00:14:52,540 --> 00:14:55,540
is just how much of this process
is trial and error,

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how different iron ores
could behave very differently.

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All the variables
of heat, of ore, of fuel

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00:15:03,620 --> 00:15:06,220
meant that the quality of your iron

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00:15:06,220 --> 00:15:09,340
depended absolutely
on the quality of your blacksmith.

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You're just hammering down to give
it a bit of a head.

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Lovely.

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That's quite satisfying.

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00:15:20,940 --> 00:15:23,140
You got some good hits in there.

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There we have our little nail.

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What a beauty! My first nail.

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00:15:29,900 --> 00:15:31,220
And it was the iron nail

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that was to underpin
the next great civilisation.

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00:15:39,620 --> 00:15:43,460
The Romans were expert
at manipulating iron.

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00:15:43,460 --> 00:15:46,500
Their blacksmiths travelled
everywhere with them,

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00:15:46,500 --> 00:15:49,580
forging the weapons
and shields of Empire.

243
00:15:53,500 --> 00:15:56,700
But the Romans never
built big with iron.

244
00:15:56,700 --> 00:16:01,260
They were limited by what the
blacksmith could do at his anvil.

245
00:16:03,980 --> 00:16:06,860
And so, we would be constrained
for another 1,500 years

246
00:16:06,860 --> 00:16:11,940
until the next great step
in our mastery of metals -

247
00:16:11,940 --> 00:16:16,380
a new technology that would unleash
the Industrial Revolution.

248
00:16:16,380 --> 00:16:20,100
Ironbridge Gorge in Shropshire was
at the heart of this new revolution.

249
00:16:20,100 --> 00:16:23,300
A man called Abraham Darby
started making iron pots

250
00:16:23,300 --> 00:16:25,420
and, almost overnight,

251
00:16:25,420 --> 00:16:29,540
he turned this sleepy valley
into the iron capital of England.

252
00:16:34,140 --> 00:16:36,500
The key was the fuel.

253
00:16:36,500 --> 00:16:40,060
Darby realised that,
with fires made from coke,

254
00:16:40,060 --> 00:16:43,420
partially burned coal, he could
reach much higher temperatures.

255
00:16:43,420 --> 00:16:46,860
And that would do something
that would transform iron.

256
00:16:51,980 --> 00:16:54,380
When it got hot enough,
something happened

257
00:16:54,380 --> 00:16:56,980
that opened up
vast new possibilities for iron.

258
00:16:56,980 --> 00:16:58,820
It melted and became liquid.

259
00:17:00,540 --> 00:17:04,340
This was the birth of a new
type of iron - cast iron.

260
00:17:10,500 --> 00:17:13,620
18th century engineers
must barely have been able

261
00:17:13,620 --> 00:17:15,500
to contain their excitement.

262
00:17:15,500 --> 00:17:19,740
Now, instead of working
iron at an anvil,

263
00:17:19,740 --> 00:17:22,380
they could pour it into a mould.

264
00:17:22,380 --> 00:17:25,540
And the mould could be
any shape or size they wanted.

265
00:17:30,980 --> 00:17:34,980
Darby's furnaces
worked around the clock.

266
00:17:34,980 --> 00:17:36,660
They turned the night sky red.

267
00:17:36,660 --> 00:17:40,180
And the roar could be
heard for miles around.

268
00:17:40,180 --> 00:17:44,620
There seemed no limit to what this
exuberant new industry could do.

269
00:17:44,620 --> 00:17:49,020
And this was proof of it. It was
built by Abraham Darby's grandson.

270
00:17:49,020 --> 00:17:52,740
And it was the first iron
bridge in the world.

271
00:18:08,220 --> 00:18:10,140
This was a golden
age of engineering,

272
00:18:10,140 --> 00:18:14,100
when it seemed only our imaginations
could limit us.

273
00:18:14,100 --> 00:18:16,620
We crossed whole countries
with iron railways.

274
00:18:16,620 --> 00:18:18,660
We crossed rivers with iron bridges.

275
00:18:18,660 --> 00:18:20,700
TRAIN WHISTLE SOUNDS

276
00:18:20,700 --> 00:18:23,940
The engineers of
the industrial world

277
00:18:23,940 --> 00:18:27,900
were seduced into thinking that
their every ambition was achievable.

278
00:18:30,780 --> 00:18:34,500
But, the dreams were
about to come crashing down.

279
00:18:34,500 --> 00:18:39,180
On 1st June, 1878, the great
and the good of Victorian Britain

280
00:18:39,180 --> 00:18:43,660
were assembled by the banks
of the River Tay here in Dundee

281
00:18:43,660 --> 00:18:47,580
to applaud the opening of
the longest bridge in the world.

282
00:18:57,660 --> 00:19:00,100
It had been
designed by Thomas Bouch,

283
00:19:00,100 --> 00:19:03,340
an ambitious railway engineer,
who may have considered

284
00:19:03,340 --> 00:19:06,340
the Tay Bridge a stepping stone
to a knighthood.

285
00:19:08,460 --> 00:19:12,420
But, one dark winter's night
in 1879 would change all that.

286
00:19:14,540 --> 00:19:18,100
A train left Edinburgh, north,
on the Aberdeen line.

287
00:19:18,100 --> 00:19:21,140
Storms were raging
across the country.

288
00:19:21,140 --> 00:19:23,100
And when the train got to the Tay,

289
00:19:23,100 --> 00:19:27,340
gale force winds were
ripping through here.

290
00:19:27,340 --> 00:19:30,820
As the train crossed the bridge,
something terrible happened.

291
00:19:30,820 --> 00:19:35,220
The iron girders cracked,
and the bridge collapsed.

292
00:19:35,220 --> 00:19:38,100
The train plunged
into the icy waters.

293
00:19:39,780 --> 00:19:41,500
There were no survivors.

294
00:19:43,380 --> 00:19:46,020
It was a terrible human tragedy.

295
00:19:46,020 --> 00:19:50,100
But what made it worse was that
it was a man-made tragedy.

296
00:19:50,100 --> 00:19:53,060
The pinnacle of our engineering
achievement,

297
00:19:53,060 --> 00:19:55,060
the iron bridge, had failed.

298
00:19:58,180 --> 00:20:01,340
Nobody had any idea why.

299
00:20:01,340 --> 00:20:03,460
It was a Victorian mystery.

300
00:20:18,220 --> 00:20:22,460
I asked Rhona Rogers,
from Dundee Museum,
how events unfolded that night.

301
00:20:22,460 --> 00:20:27,020
A couple of hours after the train
had plunged into the water,

302
00:20:27,020 --> 00:20:30,580
crowds began to gather on
the north side of the bridge.

303
00:20:30,580 --> 00:20:34,140
People looking for loved ones
that were expected home

304
00:20:34,140 --> 00:20:37,380
waited for news with none coming.

305
00:20:37,380 --> 00:20:40,660
Tell me about Thomas Bouch,
how did he react?

306
00:20:40,660 --> 00:20:43,740
He was on the boat the next day
that went out

307
00:20:43,740 --> 00:20:47,300
to look for survivors
or any signs of the wreckage,

308
00:20:47,300 --> 00:20:50,820
and he was described as being
in a very sorry state.

309
00:20:50,820 --> 00:20:56,300
And he rapidly became very ill and
then died a couple of months later.

310
00:20:56,300 --> 00:21:01,780
He died from water on the lung,
that's the official cause of death,

311
00:21:01,780 --> 00:21:05,420
but a lot of people say it was
shame and stress,

312
00:21:05,420 --> 00:21:08,900
the shame and stress of what had
happened, about his loss of career

313
00:21:08,900 --> 00:21:12,380
and not becoming the success in life
he had wanted.

314
00:21:12,380 --> 00:21:15,580
How did the rest of the country
react?

315
00:21:15,580 --> 00:21:17,220
Was it just a local tragedy?

316
00:21:17,220 --> 00:21:21,580
No, it was the longest bridge of
its type at this time in the world,

317
00:21:21,580 --> 00:21:24,740
so reactions were global.

318
00:21:24,740 --> 00:21:27,980
It affected engineering
on a world scale.

319
00:21:27,980 --> 00:21:31,060
And it was a very personal
thing for people in Dundee.

320
00:21:31,060 --> 00:21:34,660
Quite significant, isn't it,
that you can still see
the remnants of the bridge now?

321
00:21:34,660 --> 00:21:37,140
They're like tombstones,
aren't they?

322
00:21:37,140 --> 00:21:39,900
Yes, a permanent memorial
to the dead, yes,

323
00:21:39,900 --> 00:21:44,820
the 75 who lost their lives,
of which only 45 were washed ashore.

324
00:21:46,420 --> 00:21:51,220
The cornerstone of the
Industrial Revolution - cast iron -

325
00:21:51,220 --> 00:21:53,780
had failed catastrophically.

326
00:21:53,780 --> 00:21:57,340
Now the burning question was, why?

327
00:21:59,900 --> 00:22:02,500
In the immediate aftermath
of the disaster,

328
00:22:02,500 --> 00:22:05,180
there were many theories
as to what had gone wrong.

329
00:22:05,180 --> 00:22:08,460
I've come to Sheffield University
to test my own theory.

330
00:22:11,260 --> 00:22:15,540
Postgraduate students Ben Thomas
and Lucy Johnson have designed

331
00:22:15,540 --> 00:22:18,980
and built a scale model of one
of the bridge's iron pillars,

332
00:22:18,980 --> 00:22:21,620
and we're going to put it
to the test.

333
00:22:23,700 --> 00:22:27,620
So, just like in the real structure,
you had these cast irons
and this cross brace stuff

334
00:22:27,620 --> 00:22:31,980
is exactly how the piers of this
railway bridge were constructed?
Yeah.

335
00:22:31,980 --> 00:22:35,900
'The corners of each pier of the
bridge were made of cast iron,

336
00:22:35,900 --> 00:22:38,500
'and that's what
we're testing today.

337
00:22:39,940 --> 00:22:44,540
'The first test is to see how good
the pillar is at carrying
loads under compression.'

338
00:22:46,380 --> 00:22:50,900
'Could the cast iron have collapsed
just under the weight of the train?'

339
00:22:50,900 --> 00:22:54,140
Cast iron's supposed to be quite
strong in compression,

340
00:22:54,140 --> 00:22:57,460
so we've got a very simple
compression test
straight through the middle here.

341
00:22:59,180 --> 00:23:02,340
'We started to apply
pressure to the model.

342
00:23:02,340 --> 00:23:05,580
'But before the pillar gave way,
this happened...'

343
00:23:05,580 --> 00:23:07,340
LOUD METALLIC CLANG

344
00:23:07,340 --> 00:23:12,620
Oh dear, what was that?
What happened there?

345
00:23:12,620 --> 00:23:16,220
There's no obvious breaks,
which is good news.

346
00:23:16,220 --> 00:23:20,900
It may be that it started to crack
up here on the test rig.

347
00:23:20,900 --> 00:23:22,060
Really?

348
00:23:22,060 --> 00:23:26,180
So we might have broken the test
rig... No, don't say that!

349
00:23:26,180 --> 00:23:27,860
Lucy, give me hope.

350
00:23:27,860 --> 00:23:32,820
We can't see that anything's
obviously broken with
the bridge itself. OK.

351
00:23:32,820 --> 00:23:35,940
So, the good news is that the bridge
is stronger than our test rig?

352
00:23:35,940 --> 00:23:37,580
It looks that way, yeah.

353
00:23:37,580 --> 00:23:40,820
'Cast iron is known to be strong
under compression,

354
00:23:40,820 --> 00:23:45,540
'and the bridge had taken the weight
of the train many times before.

355
00:23:45,540 --> 00:23:48,660
'But there were other forces at play
on the bridge that night,

356
00:23:48,660 --> 00:23:51,220
'not least the strong winds.'

357
00:23:51,220 --> 00:23:55,700
So, because of the wind, the gale
force winds, there were forces

358
00:23:55,700 --> 00:23:59,940
on these cast iron struts that
would be making them bend that way.

359
00:23:59,940 --> 00:24:02,700
They were all trying to bend
over like a tree in the wind,

360
00:24:02,700 --> 00:24:06,620
and the question is, can that
material take that kind of force?

361
00:24:07,780 --> 00:24:11,260
'In that situation, one side
of the bridge will be compressed,

362
00:24:11,260 --> 00:24:14,340
'but the other side will stretch.

363
00:24:14,340 --> 00:24:17,620
'So I took a single bar
from the model

364
00:24:17,620 --> 00:24:20,820
'and this time I put it in a machine
that tests the metal under tension.

365
00:24:22,140 --> 00:24:24,900
'I'm going to see what happens
when you stretch it.'

366
00:24:26,500 --> 00:24:27,540
BANG

367
00:24:27,540 --> 00:24:30,220
'With very little force, it snaps.'

368
00:24:32,660 --> 00:24:37,260
'At the point where the bar broke
is evidence of what
makes cast-iron weak.'

369
00:24:37,260 --> 00:24:41,580
Look at where it's fractured.
There's this enormous hole there.

370
00:24:41,580 --> 00:24:46,020
That is an impurity
in the material which has
very little strength,

371
00:24:46,020 --> 00:24:49,100
and when you use a microscope
to look at this material

372
00:24:49,100 --> 00:24:52,940
you see not only big flaws in it,
like these strange holes,

373
00:24:52,940 --> 00:24:57,420
but deep inside the metal there
are loads of little black blobs,

374
00:24:57,420 --> 00:25:02,060
black-grey blobs, and they are
a material called graphite.

375
00:25:02,060 --> 00:25:06,940
They're embedded in the material,
and there's no way to remove them,

376
00:25:06,940 --> 00:25:10,580
you can make them smaller but they
are always going to be in cast iron.

377
00:25:11,700 --> 00:25:16,180
It's the very process of making
cast iron that causes its weakness.

378
00:25:16,180 --> 00:25:19,540
The casting process
traps in many of the impurities

379
00:25:19,540 --> 00:25:22,180
that a blacksmith
would have hammered out.

380
00:25:24,020 --> 00:25:27,620
The most important one is
graphite - carbon.

381
00:25:29,900 --> 00:25:34,660
It forms lumps that sit within
the microstructure of the metal.

382
00:25:34,660 --> 00:25:37,300
And it's these lumps
that make the metal weak.

383
00:25:38,620 --> 00:25:40,460
This is what graphite looks like.

384
00:25:40,460 --> 00:25:43,300
You know it, because
it's the stuff of your pencil.

385
00:25:43,300 --> 00:25:44,740
It's a very weak material,

386
00:25:44,740 --> 00:25:49,500
so if you have loads of this stuff
embedded in your iron,

387
00:25:49,500 --> 00:25:52,860
it's not surprising that
that iron is going to be weak.

388
00:25:53,980 --> 00:25:58,500
But back in the 19th century,
this interior world of metals

389
00:25:58,500 --> 00:26:00,380
was still hidden from us.

390
00:26:04,260 --> 00:26:07,900
What it comes down to is this -
we were building bridges out of iron

391
00:26:07,900 --> 00:26:10,420
without fully
understanding the material.

392
00:26:10,420 --> 00:26:12,980
We needed to change our relationship
with metal

393
00:26:12,980 --> 00:26:15,420
from one of mastery
to one of understanding.

394
00:26:17,260 --> 00:26:20,820
All we really knew was that
cast iron had failed us.

395
00:26:20,820 --> 00:26:23,740
We desperately needed
a stronger metal.

396
00:26:24,820 --> 00:26:27,980
But the answer wouldn't lie in
making the purist iron possible.

397
00:26:27,980 --> 00:26:31,460
It would turn out to be far
more complex.

398
00:26:34,620 --> 00:26:38,940
The Victorian engineers looked
to history for the strongest
iron they could find.

399
00:26:40,980 --> 00:26:45,300
The metal smiths of old used it to
make swords of legendary strength.

400
00:26:46,660 --> 00:26:48,900
They called it 'good iron'.

401
00:26:48,900 --> 00:26:51,020
We call it steel.

402
00:26:54,380 --> 00:26:59,300
Back in the forge, Owen is going to
reveal the secret of good iron -

403
00:26:59,300 --> 00:27:02,740
making the iron pure,
but not too pure.

404
00:27:04,340 --> 00:27:07,620
Following the techniques
of ancient swordsmiths,

405
00:27:07,620 --> 00:27:12,260
he hammers the iron and then folds,
and heats and folds again,

406
00:27:12,260 --> 00:27:16,580
exposing more and more
of the iron to the air,
so the impurities burn away.

407
00:27:20,220 --> 00:27:22,980
So I'm just going to
cut it in half...

408
00:27:25,580 --> 00:27:27,140
Then bend it back on itself.

409
00:27:30,980 --> 00:27:32,420
Back in the fire.

410
00:27:32,420 --> 00:27:35,460
We had four layers,
now we've got eight, next fold 16.

411
00:27:35,460 --> 00:27:39,060
If this was to be the edge material
of the blade I'd probably

412
00:27:39,060 --> 00:27:41,900
take it up to somewhere between 700
and couple of thousand layers.

413
00:27:41,900 --> 00:27:43,500
A thousand layers?

414
00:27:50,580 --> 00:27:53,980
So what's coming off the edge there?
That's iron oxide.

415
00:27:53,980 --> 00:27:55,580
So that's its skin, really? Yeah.

416
00:27:58,380 --> 00:28:03,060
'Through a combination of skill
and experience the swordsmiths knew

417
00:28:03,060 --> 00:28:06,900
'when their metal was pure enough
to hammer into a blade.

418
00:28:08,140 --> 00:28:12,180
'Then they added at touch of magic
- it's called quenching.

419
00:28:14,420 --> 00:28:17,060
'They thrust the red hot
blade into a cooling liquid.

420
00:28:20,140 --> 00:28:23,980
'When they drew it out again
the edge had hardened.'

421
00:28:25,020 --> 00:28:28,020
When you read the accounts
written down about this process,

422
00:28:28,020 --> 00:28:32,020
you find all sorts
of weird materials,

423
00:28:32,020 --> 00:28:36,860
like, people would get the urine
of a redheaded boy,

424
00:28:36,860 --> 00:28:41,060
or they'd get a goat which had
only fed on the fern for three days

425
00:28:41,060 --> 00:28:44,300
and they would quench into that -
what do you think about this?

426
00:28:44,300 --> 00:28:50,700
If it worked, if your master smith
taught you to quench in the urine
of a redheaded boy,

427
00:28:50,700 --> 00:28:54,660
then if it worked for him there's
no reason why you'd stop.

428
00:28:54,660 --> 00:28:56,460
And, also it adds mystique,
doesn't it?

429
00:28:56,460 --> 00:29:00,620
'Technique and temperature
worked a mysterious alchemy,

430
00:29:00,620 --> 00:29:04,220
'creating a metal
that kept its sharp edge.

431
00:29:04,220 --> 00:29:07,540
'A metal with almost magical
properties.'

432
00:29:08,980 --> 00:29:12,940
The master swordsmiths
had manipulated iron so skilfully

433
00:29:12,940 --> 00:29:16,580
they had unwittingly
created a totally new metal.

434
00:29:16,580 --> 00:29:18,420
Steel.

435
00:29:18,420 --> 00:29:21,860
The strong, reliable metal
the Victorian engineers needed

436
00:29:21,860 --> 00:29:24,300
to fulfil their growing ambitions.

437
00:29:26,860 --> 00:29:29,780
But the problem is,
as we've just seen,

438
00:29:29,780 --> 00:29:33,540
it takes a huge amount of time,
effort, expertise,

439
00:29:33,540 --> 00:29:36,100
to just make this one, small blade.

440
00:29:36,100 --> 00:29:38,340
So, if the Victorians
were going to use steel,

441
00:29:38,340 --> 00:29:41,460
they were going to have to learn
how to mass-produce it.

442
00:29:41,460 --> 00:29:46,100
And in order to do that they would
have to find out what was
going on inside this metal.

443
00:29:47,780 --> 00:29:52,540
A clue would come from another
feature of the swordsmith's art.

444
00:29:52,540 --> 00:29:57,020
The pattern of the sword was
the must-have mark of quality.

445
00:29:58,340 --> 00:30:02,180
Dipping the swords in acid made
the intricate swirling patterns,

446
00:30:02,180 --> 00:30:07,180
created by the folding, twisting and
hammering, become more pronounced.

447
00:30:08,540 --> 00:30:11,020
This process was called etching.

448
00:30:12,460 --> 00:30:17,500
And etching would be the key
to revealing the secret of steel,

449
00:30:17,500 --> 00:30:19,740
exactly what it was made of.

450
00:30:20,860 --> 00:30:26,660
Here in Sheffield, in 1863,
the single-minded dedication

451
00:30:26,660 --> 00:30:30,340
of one man provided the flash
of insight that changed everything.

452
00:30:32,780 --> 00:30:37,420
Henry Clifton Sorby was perhaps
the last great scientific amateur

453
00:30:37,420 --> 00:30:42,140
in an age when science was becoming
the concern of professionals.

454
00:30:42,140 --> 00:30:47,620
Sorby pretty much invented
the idea of looking at metals
through microscopes.

455
00:30:47,620 --> 00:30:50,540
He was ridiculed by his colleagues.

456
00:30:52,060 --> 00:30:55,220
But he persevered,
and it's lucky for as he did.

457
00:30:55,220 --> 00:30:58,340
Here, I'm proud to say,
I have in front of me

458
00:30:58,340 --> 00:31:00,980
the original samples he first made.

459
00:31:02,300 --> 00:31:05,900
Sorby prepared his steel
samples in exactly the same way

460
00:31:05,900 --> 00:31:09,500
as the ancient sword Smiths -
he etched them.

461
00:31:11,060 --> 00:31:15,220
And when he looked at the intricate
patterns under the microscope,

462
00:31:15,220 --> 00:31:18,100
Sorby discovered
the secret of steel's strength.

463
00:31:19,980 --> 00:31:23,820
This is a 150-year-old
sample that he prepared.

464
00:31:23,820 --> 00:31:28,620
Let me show you what he saw
and no-one else had ever seen.

465
00:31:29,820 --> 00:31:37,020
The microscope revealed that steel
was a very pure form of iron,
much purer than cast-iron.

466
00:31:37,020 --> 00:31:40,380
But there's still a small
amount of impurity there.

467
00:31:40,380 --> 00:31:44,660
The dark bits that look like rivers
are crystals that contain carbon.

468
00:31:45,900 --> 00:31:50,220
It turned out the whole premise
of the iron industry had been false.

469
00:31:50,220 --> 00:31:54,260
Everyone had thought that
what you had to do was beat out
the impurities -

470
00:31:54,260 --> 00:31:56,660
the purer the iron you could get
the better it would be -

471
00:31:56,660 --> 00:31:57,860
And they were wrong.

472
00:31:59,700 --> 00:32:04,780
Instead, what was needed
was precisely the right amount
of impurity.

473
00:32:04,780 --> 00:32:09,220
An alloy of iron and carbon
in exactly the right proportions.

474
00:32:13,580 --> 00:32:16,340
This is the crystal
lattice of pure iron.

475
00:32:18,460 --> 00:32:20,220
And this is steel.

476
00:32:21,660 --> 00:32:24,540
Carbon atoms sit in the gaps
between the iron atoms,

477
00:32:24,540 --> 00:32:26,300
making steel much stronger.

478
00:32:27,740 --> 00:32:31,180
But you have to have just
the right amount of carbon.

479
00:32:34,020 --> 00:32:37,260
In cast iron,
there's too much carbon

480
00:32:37,260 --> 00:32:41,140
and the spare carbon atoms form
larger blobs within the crystal

481
00:32:41,140 --> 00:32:43,020
and make the metal weaker.

482
00:32:50,380 --> 00:32:53,380
Now we knew what made steel
so strong.

483
00:32:55,140 --> 00:32:58,180
But we were still in the dark
about how to produce it cheaply

484
00:32:58,180 --> 00:33:02,740
and on the industrial scale
that the 19th-century demanded.

485
00:33:03,900 --> 00:33:07,740
One day, a Sheffield-based engineer
called Henry Bessemer

486
00:33:07,740 --> 00:33:11,060
stood up at a British science
meeting and shocked his audience

487
00:33:11,060 --> 00:33:13,940
by announcing he could
mass-produce steel.

488
00:33:13,940 --> 00:33:18,380
It required no hammering,
no beating, no folding.

489
00:33:18,380 --> 00:33:23,580
He could make tonnes of the stuff
in this, his Bessemer converter.

490
00:33:28,300 --> 00:33:33,140
This huge bucket that Bessemer
designed would have contained

491
00:33:33,140 --> 00:33:35,180
an enormous amount of molten iron,

492
00:33:35,180 --> 00:33:38,460
and that, of course,
was full of carbon.

493
00:33:38,460 --> 00:33:43,260
So what Bessemer suggested was
that you made this pipe that
goes down the bottom here,

494
00:33:43,260 --> 00:33:46,780
and they pumped air
through the liquid iron,

495
00:33:46,780 --> 00:33:50,220
and that air contained oxygen,
and the oxygen reacted

496
00:33:50,220 --> 00:33:53,780
with the carbon to create
carbon dioxide.

497
00:33:53,780 --> 00:33:57,820
And Bessemer's idea was to just
do that long enough to get

498
00:33:57,820 --> 00:34:00,980
the carbon content of the iron
down to about 1%.

499
00:34:00,980 --> 00:34:04,660
And he designed these enormous
cranks on the side here,

500
00:34:04,660 --> 00:34:08,700
so when the carbon content
of the steel is exactly right

501
00:34:08,700 --> 00:34:12,140
you just crank the whole bucket
over and out pours masses

502
00:34:12,140 --> 00:34:15,420
and masses of this
beautiful, liquid steel.

503
00:34:20,500 --> 00:34:25,380
'I'm going to make steel
in a way that's based
on Bessemer's principle.

504
00:34:25,380 --> 00:34:30,620
'Molten iron, which is
full of impurities like carbon,
is poured into a bucket.

505
00:34:30,620 --> 00:34:33,300
'I blow oxygen through it,

506
00:34:33,300 --> 00:34:36,460
'just as air was blown
through Bessemer's converter.

507
00:34:36,460 --> 00:34:39,940
'The oxygen reacts with a carbon
to form carbon dioxide,

508
00:34:39,940 --> 00:34:42,940
'removing most of the carbon.

509
00:34:42,940 --> 00:34:48,100
'So you should be left with
just the right amount of carbon
to make steel.'

510
00:34:49,820 --> 00:34:52,580
Well, the process may be simple,
but it's insane.

511
00:34:52,580 --> 00:34:56,620
I mean you are pumping oxygen
or air through a liquid metal,

512
00:34:56,620 --> 00:35:00,100
and it gets white hot
and it's bubbling and you think,

513
00:35:00,100 --> 00:35:02,260
this is fine,
making a small cauldron of it,

514
00:35:02,260 --> 00:35:06,180
but imagine making a bucket load
of the stuff the size of this room!

515
00:35:06,180 --> 00:35:08,460
That's what Bessemer was doing,
and having a go at it

516
00:35:08,460 --> 00:35:12,060
I realise quite
how avant-garde he was.

517
00:35:12,060 --> 00:35:14,460
What he was proposing was
really extraordinary.

518
00:35:16,020 --> 00:35:20,380
But the process had a major
disadvantage - it just didn't work.

519
00:35:22,820 --> 00:35:26,300
It was too difficult
to hit precisely

520
00:35:26,300 --> 00:35:28,900
the right amount of carbon -
just under 1%.

521
00:35:31,180 --> 00:35:34,460
Bessemer and his converter
faced financial ruin.

522
00:35:36,820 --> 00:35:38,660
But not for long.

523
00:35:39,780 --> 00:35:44,780
British metallurgist Robert Forester
Mushet came to his rescue.

524
00:35:47,220 --> 00:35:50,660
He suggested they should
remove all the carbon

525
00:35:50,660 --> 00:35:53,300
and then add 1% back in.

526
00:35:55,340 --> 00:35:56,540
It worked.

527
00:36:00,220 --> 00:36:04,900
For the first time we could
mass-produce high-quality steel.

528
00:36:04,900 --> 00:36:07,020
We now had a metal
that was strong enough

529
00:36:07,020 --> 00:36:10,140
and tough enough
to fulfil our ambitions.

530
00:36:14,300 --> 00:36:17,100
The breakthrough
made Bessemer's name,

531
00:36:17,100 --> 00:36:21,060
but he had to be forced
to acknowledge the part
Mushet had played.

532
00:36:23,540 --> 00:36:26,620
In the end,
Bessemer had to agree to pay him

533
00:36:26,620 --> 00:36:29,380
£300 a year for
the rest of his life.

534
00:36:31,500 --> 00:36:36,900
With mass-produced steel we'd
cracked the problem of strength.

535
00:36:36,900 --> 00:36:39,420
90% of the metal
we make today is steel.

536
00:36:42,540 --> 00:36:47,300
It's allowed as to travel across the
globe by rail...

537
00:36:47,300 --> 00:36:49,220
..by road...

538
00:36:49,220 --> 00:36:51,460
..and by sea.

539
00:36:51,460 --> 00:36:56,860
Strong, reliable steel enabled us
to build great cities.

540
00:36:56,860 --> 00:37:00,100
The construction industry
would be nowhere without steel,

541
00:37:00,100 --> 00:37:04,980
and the destruction industry
benefited just as much.

542
00:37:08,140 --> 00:37:12,100
But steel was not the answer
to all our ambitions.

543
00:37:12,100 --> 00:37:15,740
Aluminium would be
the metal of the next century.

544
00:37:17,420 --> 00:37:21,660
The century when the secret
inner world of metals would
finally be revealed.

545
00:37:23,460 --> 00:37:27,340
The thing about metals is
they all look roughly the same.

546
00:37:27,340 --> 00:37:30,940
But they're not the same.
This is steel and this is aluminium.

547
00:37:33,860 --> 00:37:36,700
Aluminium is three times
lighter than steel.

548
00:37:39,620 --> 00:37:43,580
Here was the perfect metal
to take us into the next age -

549
00:37:43,580 --> 00:37:46,020
the age of flight.

550
00:37:46,020 --> 00:37:50,700
Except for one thing - aluminium
is just not strong enough.

551
00:37:53,700 --> 00:37:58,780
Scientists around the world
began to look for ways to make
aluminium stronger.

552
00:38:00,020 --> 00:38:03,460
Among them was the German
metallurgist, Alfred Wilm.

553
00:38:05,340 --> 00:38:11,060
Wilm knew that our ancestors
had strengthened copper by mixing
it with tin,

554
00:38:11,060 --> 00:38:16,700
and what made steel strong
was having the right combination
of iron and carbon.

555
00:38:16,700 --> 00:38:21,180
So, he set about mixing aluminium
with other metals.

556
00:38:22,900 --> 00:38:26,540
He finally ended up with
an alloy of aluminium, copper,

557
00:38:26,540 --> 00:38:28,860
manganese and magnesium.

558
00:38:28,860 --> 00:38:30,500
He named it duralumin.

559
00:38:32,420 --> 00:38:35,380
And then he thought, when you want
to make really hard steel,

560
00:38:35,380 --> 00:38:38,180
what you do is you quench it,
so he took those alloys

561
00:38:38,180 --> 00:38:41,860
and he put them
in a furnace and he quenched them.

562
00:38:41,860 --> 00:38:43,500
Here it is...

563
00:38:44,740 --> 00:38:47,940
..and I'm going to quench it.

564
00:38:51,340 --> 00:38:56,820
Now, once he'd quenched the alloys
the moment of truth came.

565
00:38:58,540 --> 00:39:01,660
Would it be as strong as steel?

566
00:39:05,820 --> 00:39:07,220
No.

567
00:39:08,660 --> 00:39:12,780
And this happened time and time
and time and time again.

568
00:39:14,180 --> 00:39:17,500
Until he could take
the disappointment no more.

569
00:39:17,500 --> 00:39:20,260
He stormed out of his lab and...

570
00:39:20,260 --> 00:39:23,140
..went boating for a few days.

571
00:39:25,540 --> 00:39:28,780
But while he was
messing about on the river,

572
00:39:28,780 --> 00:39:31,660
something remarkable happened.

573
00:39:31,660 --> 00:39:36,740
Something that Wilm had neither
planned nor even imagined possible.

574
00:39:36,740 --> 00:39:39,100
This is the same alloy.

575
00:39:39,100 --> 00:39:42,620
The only differences is it's a week
later now, and watch this.

576
00:39:45,860 --> 00:39:47,700
It's much, much stronger.

577
00:39:50,300 --> 00:39:55,020
'And this is what Wilm found when
he returned from his boating trip.

578
00:39:55,020 --> 00:39:59,100
'Without Wilm lifting a finger,
his alloy had transformed itself

579
00:39:59,100 --> 00:40:03,100
'from a weak, bendy substance
into a strong, rigid one.

580
00:40:04,740 --> 00:40:07,580
'It was almost as though
the lump of inert metal

581
00:40:07,580 --> 00:40:13,300
'he had left behind was a living
thing that had changed over time.

582
00:40:13,300 --> 00:40:15,220
'It had grown harder as it aged.'

583
00:40:17,180 --> 00:40:20,180
What Wilm had discovered was
something called age hardening.

584
00:40:20,180 --> 00:40:21,820
Let me show you how it works.

585
00:40:21,820 --> 00:40:24,620
So, if this is a crystal
of aluminium,

586
00:40:24,620 --> 00:40:27,500
we know that's really soft.

587
00:40:27,500 --> 00:40:30,100
What we need is something
that's going to make it stronger.

588
00:40:30,100 --> 00:40:33,660
Actually, he'd found an alloy
which, when you leave it over time,

589
00:40:33,660 --> 00:40:38,180
tiny little crystals
grow inside the aluminium crystals.

590
00:40:38,180 --> 00:40:43,180
They emerge out of a kind
of atomistic mist, and it's those

591
00:40:43,180 --> 00:40:47,820
that harden the crystal, they make
it stronger, they reinforce it.

592
00:40:53,300 --> 00:40:56,660
As new crystals grow,
they interfere with the lattice,

593
00:40:56,660 --> 00:41:00,820
and the aluminium alloy's ability
to shuffle atoms and change shape.

594
00:41:01,860 --> 00:41:03,900
This makes it harder and stronger.

595
00:41:09,340 --> 00:41:12,700
Wilm had solved the problem of
how to make aluminium stronger.

596
00:41:14,340 --> 00:41:18,900
And he had also revealed metals to
be mutable, almost living materials.

597
00:41:20,420 --> 00:41:25,820
So many of the great discoveries
of science come by happy accident.

598
00:41:25,820 --> 00:41:30,740
From Alfred Wilm's despair
came a new understanding of metals,

599
00:41:30,740 --> 00:41:35,020
an understanding that would finally
allow us to conquer the skies.

600
00:41:38,460 --> 00:41:45,100
His alloy, duralumin, was used to
make the fuselage of the Spitfire -

601
00:41:45,100 --> 00:41:50,180
the only Allied aircraft to remain
a front line fighter throughout
the Second World War.

602
00:41:52,420 --> 00:41:56,460
War forced the pace,
with new and better alloys.

603
00:41:56,460 --> 00:41:59,180
Peacetime brought the desire
for passenger flight.

604
00:42:00,420 --> 00:42:04,060
We were about to push metals
harder than ever before.

605
00:42:08,860 --> 00:42:14,180
In great secrecy, the De Havilland
company here in Hertfordshire

606
00:42:14,180 --> 00:42:19,860
embarked on an ambitious plan
to build the world's first
commercial jet aircraft,

607
00:42:19,860 --> 00:42:24,420
to tame and harness changeable,
mutable metal

608
00:42:24,420 --> 00:42:28,180
and build a plane strong
and reliable enough

609
00:42:28,180 --> 00:42:31,780
to soar twice as high as man
had gone before.

610
00:42:34,980 --> 00:42:37,900
The plane was
the ultimate in modern technology.

611
00:42:37,900 --> 00:42:42,580
It went higher and faster,
and boasted a pressurised cabin

612
00:42:42,580 --> 00:42:46,700
for the comfort of the jet age
passengers and crew.

613
00:42:46,700 --> 00:42:49,780
It was also the most tested
aircraft of its time.

614
00:42:54,380 --> 00:42:59,420
Mike Ramsden was one of
the test engineers on this,

615
00:42:59,420 --> 00:43:01,060
'the De Havilland Comet.'

616
00:43:01,060 --> 00:43:04,340
Can you remember the moment
when you stood on an airfield

617
00:43:04,340 --> 00:43:07,780
looking at this Comet taking off,
the comet you'd tested?

618
00:43:07,780 --> 00:43:09,820
It was...

619
00:43:09,820 --> 00:43:14,980
It was like watching something
from outer space, it was so...

620
00:43:14,980 --> 00:43:18,860
..new, and it sounds corny,
doesn't it?

621
00:43:18,860 --> 00:43:21,980
But there was nothing
else like it in the world.

622
00:43:21,980 --> 00:43:25,220
When the crew were up
at double the height

623
00:43:25,220 --> 00:43:28,460
and double the speed of propeller
airliners,

624
00:43:28,460 --> 00:43:30,940
they just couldn't believe it,

625
00:43:30,940 --> 00:43:34,580
being able to see both sides
of the Channel at the same time.

626
00:43:34,580 --> 00:43:36,620
And flying high,
you had pressurised the cabin.

627
00:43:37,660 --> 00:43:41,660
Yes, this was a very big
engineering challenge.

628
00:43:41,660 --> 00:43:44,340
To pressurise the fuselage

629
00:43:44,340 --> 00:43:49,100
so that human beings could
survive at that height.

630
00:43:59,540 --> 00:44:01,780
It was the way to go,
it was the way to fly.

631
00:44:01,780 --> 00:44:03,900
It was the way to arrive.

632
00:44:08,020 --> 00:44:11,540
It seemed that a golden age
of air travel had dawned.

633
00:44:13,180 --> 00:44:16,380
But it was about to
turn to disaster.

634
00:44:19,260 --> 00:44:23,380
A year to the day after
the first passenger flight,

635
00:44:23,380 --> 00:44:27,700
a Comet disintegrated in midair,
killing everybody on board.

636
00:44:29,140 --> 00:44:33,460
Within months, two more Comets
had crashed into the Mediterranean.

637
00:44:33,460 --> 00:44:35,500
The entire fleet was grounded.

638
00:44:37,580 --> 00:44:41,020
There was something
going on at the heart of metal
we didn't understand.

639
00:44:42,660 --> 00:44:44,860
Did the whole staff,
you and all your workmates,

640
00:44:44,860 --> 00:44:47,700
did you all feel responsible?

641
00:44:47,700 --> 00:44:52,780
Did we feel guilty,
you mean, of killing 100 people?

642
00:44:52,780 --> 00:44:55,100
Yes, is the short answer.

643
00:45:06,140 --> 00:45:08,380
Finding the cause was now
the priority for Mike

644
00:45:08,380 --> 00:45:10,060
and his colleagues.

645
00:45:10,060 --> 00:45:13,900
They knew metal
was a mutable material,

646
00:45:13,900 --> 00:45:18,540
that it could suffer from a damaging
phenomenon called metal fatigue.

647
00:45:18,540 --> 00:45:20,900
They had tested
extensively for this.

648
00:45:23,020 --> 00:45:25,700
But what they couldn't predict
were the effects

649
00:45:25,700 --> 00:45:28,940
of this extreme new environment
and the pressurising

650
00:45:28,940 --> 00:45:33,260
and de-pressurising of the cabin
needed for high altitude flight.

651
00:45:36,660 --> 00:45:38,700
The real problem was
a combination of factors,

652
00:45:38,700 --> 00:45:42,380
one of which was that this aircraft
had to go higher

653
00:45:42,380 --> 00:45:46,820
than ever before, up five miles
high, which caused a compression

654
00:45:46,820 --> 00:45:48,860
and decompression of the fuselage,

655
00:45:48,860 --> 00:45:51,820
so you have it almost
breathing in and out, in and out,

656
00:45:51,820 --> 00:45:53,740
every time it takes off and lands.

657
00:45:55,940 --> 00:45:59,620
The stress of constant
pressurisation and de-pressurisation

658
00:45:59,620 --> 00:46:01,540
eventually tolled on this aeroplane.

659
00:46:04,060 --> 00:46:06,620
Metal will break
if you bend it often enough.

660
00:46:06,620 --> 00:46:10,380
In the Comet's fuselage,
tiny fatigue cracks appeared.

661
00:46:10,380 --> 00:46:14,420
What began as a very small fracture
close to a window

662
00:46:14,420 --> 00:46:17,060
spread in to a catastrophic crack.

663
00:46:17,060 --> 00:46:19,500
The whole aircraft came
apart mid-flight.

664
00:46:19,500 --> 00:46:21,820
The cause was
a combination of metal fatigue

665
00:46:21,820 --> 00:46:25,380
and concentrations of stress
within the fuselage.

666
00:46:27,220 --> 00:46:30,780
It's a weird quirk of fate
that these windows were square

667
00:46:30,780 --> 00:46:33,340
because that's exactly
the wrong shape

668
00:46:33,340 --> 00:46:36,180
if you want to minimise
the concentration of stress.

669
00:46:36,180 --> 00:46:40,020
So at the corners the stress
is all concentrated

670
00:46:40,020 --> 00:46:42,260
and started forming little cracks,

671
00:46:42,260 --> 00:46:45,700
it was those that were
the big problem.

672
00:46:45,700 --> 00:46:48,980
Today we know that you mustn't have
square windows

673
00:46:48,980 --> 00:46:51,460
in these kind
of pressure structures.

674
00:46:51,460 --> 00:46:54,820
If you look at any aircraft today,
you'll never see a square window.

675
00:46:57,700 --> 00:46:59,740
Comet changed everything.

676
00:46:59,740 --> 00:47:02,380
New regulations would make sure
that metal was replaced

677
00:47:02,380 --> 00:47:04,380
before it became fatigued.

678
00:47:04,380 --> 00:47:07,980
But the most important lesson we
learnt was just how little we knew.

679
00:47:10,300 --> 00:47:13,540
Extreme conditions were causing
extreme reactions

680
00:47:13,540 --> 00:47:16,580
inside the metal
that we didn't understand.

681
00:47:16,580 --> 00:47:19,500
We desperately needed
to see what was happening

682
00:47:19,500 --> 00:47:22,700
deep inside the metal crystal.

683
00:47:25,740 --> 00:47:28,180
One young scientist was about
to make a breakthrough

684
00:47:28,180 --> 00:47:31,460
and I know him really well because a
few decades later

685
00:47:31,460 --> 00:47:34,380
he was one of my lecturers here
at Oxford University,

686
00:47:34,380 --> 00:47:36,500
Professor Sir Peter Hirsch.

687
00:47:40,980 --> 00:47:45,820
Hirsch's team was one of the first
to take thin foils of metal

688
00:47:45,820 --> 00:47:49,500
and look at them under a brand new
kind of microscope,

689
00:47:49,500 --> 00:47:51,860
a transmission electron microscope,

690
00:47:51,860 --> 00:47:55,340
which increased magnification
by tens of thousands.

691
00:47:55,340 --> 00:47:58,980
Hirsch would finally see inside
the metal crystal

692
00:47:58,980 --> 00:48:03,060
and what he found would send
shock waves around the world
of material science.

693
00:48:05,940 --> 00:48:07,940
Meeting up with
Professor Hirsch again,

694
00:48:07,940 --> 00:48:11,820
he explained that in the 1950s
there were theories

695
00:48:11,820 --> 00:48:15,700
about why metals behaved
as they did, but still no proof.

696
00:48:17,860 --> 00:48:21,820
What was really needed
was an experimental technique

697
00:48:21,820 --> 00:48:27,580
which was universally applicable
whereby you could see inside metals.

698
00:48:29,700 --> 00:48:32,180
And that's what Hirsch discovered.

699
00:48:32,180 --> 00:48:35,460
This is the film
he took of his original experiments.

700
00:48:35,460 --> 00:48:41,100
He saw for the first time
deep inside the metal crystal,

701
00:48:41,100 --> 00:48:43,740
where, incredibly,
the metal looked like it was alive.

702
00:48:43,740 --> 00:48:48,380
Those moving little lines and loops
are the Mexican waves of atoms

703
00:48:48,380 --> 00:48:51,460
shuffling across the metal crystal.

704
00:48:51,460 --> 00:48:54,620
They're changing
the shape of the crystal.

705
00:48:54,620 --> 00:48:57,540
Suddenly everything fell into place.

706
00:48:57,540 --> 00:49:01,060
The technique revealed
a new micro-world, if you like,

707
00:49:01,060 --> 00:49:02,980
inside a metal.

708
00:49:02,980 --> 00:49:07,100
You suddenly saw
the inside of a metal

709
00:49:07,100 --> 00:49:10,460
and all sorts of things
were revealed.

710
00:49:10,460 --> 00:49:15,860
It was very, very exciting.

711
00:49:15,860 --> 00:49:18,500
We were now in a position to prove

712
00:49:18,500 --> 00:49:20,900
what had previously
only been guessed at...

713
00:49:20,900 --> 00:49:23,860
That metals were dynamic crystals,

714
00:49:23,860 --> 00:49:25,900
that these ripples were caused
by atoms

715
00:49:25,900 --> 00:49:29,380
shuffling within the crystal,
changing the metal's shape.

716
00:49:32,100 --> 00:49:35,380
This explained
what we'd known for centuries,
but never fully understood...

717
00:49:35,380 --> 00:49:37,780
Why metal would change shape

718
00:49:37,780 --> 00:49:42,020
rather than crack
when it was hit with a hammer.

719
00:49:42,020 --> 00:49:46,700
And also why it became stronger
when it was alloyed.

720
00:49:46,700 --> 00:49:49,740
It showed that designing
the internal architecture of metal

721
00:49:49,740 --> 00:49:52,380
was the key to progress.

722
00:49:55,660 --> 00:50:01,740
Microscopy finally allowed us to
master the micro-world of metals.

723
00:50:04,260 --> 00:50:07,420
Hirsch's breakthrough reignited
our passion and belief for metals.

724
00:50:07,420 --> 00:50:09,500
We could start to design
our own metals,

725
00:50:09,500 --> 00:50:12,060
and there was a huge flowering
of metallurgy.

726
00:50:12,060 --> 00:50:15,300
There seemed to be no problem
we couldn't solve.

727
00:50:15,300 --> 00:50:18,620
'And we were facing another.

728
00:50:18,620 --> 00:50:22,380
'How to get a metal to work in the
most extreme environment on earth.

729
00:50:22,380 --> 00:50:24,900
'A jet engine.'

730
00:50:24,900 --> 00:50:27,140
Let me show you what I mean.

731
00:50:27,140 --> 00:50:28,860
Inside jet engines,

732
00:50:28,860 --> 00:50:31,540
is an incredibly difficult
place for metals to be.

733
00:50:31,540 --> 00:50:33,580
Extremely hot temperatures.

734
00:50:33,580 --> 00:50:36,060
Extremely high stress
they had to put up with.

735
00:50:36,060 --> 00:50:37,860
So they had to design a new alloy

736
00:50:37,860 --> 00:50:39,700
that could cope
with this environment.

737
00:50:39,700 --> 00:50:41,620
And it was called "superalloy".

738
00:50:41,620 --> 00:50:44,580
So-called because it was so super.

739
00:50:44,580 --> 00:50:46,140
Here's a bit of it here.

740
00:50:46,140 --> 00:50:48,260
I'm going to pit it against
our old friend steel,

741
00:50:48,260 --> 00:50:50,380
who, of course, we know and love.

742
00:50:50,380 --> 00:50:53,100
I'm going to hang weights
off these two wires.

743
00:50:53,100 --> 00:50:54,620
It's the same weight, in both cases,

744
00:50:54,620 --> 00:50:57,940
and they're the same
thickness of wire.

745
00:50:57,940 --> 00:50:59,820
So, now they're under
the same stress.

746
00:50:59,820 --> 00:51:02,420
Now, I'm going to make it
harder for them,

747
00:51:02,420 --> 00:51:05,980
because they'll have to hold that up
while under huge temperatures,

748
00:51:05,980 --> 00:51:09,660
which means me
putting a blowtorch on them.

749
00:51:09,660 --> 00:51:13,020
OK, are you guys ready? Let's go.

750
00:51:18,220 --> 00:51:21,260
So, the steel wire succumbed
within a few seconds.

751
00:51:21,260 --> 00:51:25,340
And that's only a fraction
of the heat inside a jet engine.

752
00:51:27,940 --> 00:51:31,900
I could be here all day
with the superalloy.

753
00:51:31,900 --> 00:51:33,380
This superalloy can take this.

754
00:51:35,180 --> 00:51:38,420
I know these metals all look the
same, but inside this superalloy

755
00:51:38,420 --> 00:51:40,460
is the most-exquisite
microstructure,

756
00:51:40,460 --> 00:51:44,100
that was designed for this purpose.

757
00:51:44,100 --> 00:51:46,540
To control the movement
inside the metal,

758
00:51:46,540 --> 00:51:49,780
and make it unbelievably strong
at high temperatures.

759
00:51:52,420 --> 00:51:54,980
'The cubes of material
within the superalloy

760
00:51:54,980 --> 00:51:57,380
'are called "gamma prime crystals".

761
00:51:57,380 --> 00:51:58,740
'They sit within the alloy,

762
00:51:58,740 --> 00:52:00,780
'affecting its ability
to change shape.

763
00:52:02,260 --> 00:52:04,580
'Which makes it incredibly strong,

764
00:52:04,580 --> 00:52:07,340
'even at temperatures
close to its melting point.'

765
00:52:10,100 --> 00:52:11,740
That's pretty impressive,

766
00:52:11,740 --> 00:52:14,020
and, as the jet age progressed,

767
00:52:14,020 --> 00:52:16,820
scientists and engineers
pushed the technology,

768
00:52:16,820 --> 00:52:19,820
to create more and more
powerful engines.

769
00:52:22,780 --> 00:52:25,620
'Superalloys were some
of the strongest metals

770
00:52:25,620 --> 00:52:26,940
'we had ever created.

771
00:52:26,940 --> 00:52:30,100
'But the 21st century jet engine

772
00:52:30,100 --> 00:52:31,500
'would push them to their limit.

773
00:52:31,500 --> 00:52:34,580
'In this extreme environment,

774
00:52:34,580 --> 00:52:37,420
'even superalloys
will change shape.'

775
00:52:37,420 --> 00:52:41,180
One of the things we love about
metals is their malleability.

776
00:52:41,180 --> 00:52:43,620
When it's red hot,
it behaves like plastic.

777
00:52:43,620 --> 00:52:45,860
You can make it into
whatever shape you want.

778
00:52:45,860 --> 00:52:49,820
This is wonderful stuff
to make an engine out of.

779
00:52:49,820 --> 00:52:52,980
But the problem is,
when you're making an engine

780
00:52:52,980 --> 00:52:55,380
that needs to be operating
at temperatures

781
00:52:55,380 --> 00:52:56,820
that are themselves red hot,

782
00:52:56,820 --> 00:52:59,740
deep inside the engine,
you've got engine parts

783
00:52:59,740 --> 00:53:02,140
that really mustn't change shape.

784
00:53:02,140 --> 00:53:06,780
'These turbine blades operate
at 1,700 degrees centigrade,

785
00:53:06,780 --> 00:53:08,620
'and 10,000 RPM.

786
00:53:08,620 --> 00:53:10,580
'If working in those conditions

787
00:53:10,580 --> 00:53:13,980
'made them lengthen,
even a tiny bit,

788
00:53:13,980 --> 00:53:16,420
' a phenomenon known as "creep",

789
00:53:16,420 --> 00:53:18,780
'catastrophe would follow.'

790
00:53:18,780 --> 00:53:22,020
These engines are designed
with the precision of a watchmaker.

791
00:53:22,020 --> 00:53:25,420
Here, at the back of the engine, you
can see the turbine blades rotating

792
00:53:25,420 --> 00:53:27,540
within the casing.

793
00:53:27,540 --> 00:53:30,380
If there's any creep
in those turbine blades,

794
00:53:30,380 --> 00:53:33,180
they'll hit the casing, and the
whole thing will seize up.

795
00:53:33,180 --> 00:53:34,580
And that must not happen.

796
00:53:34,580 --> 00:53:37,860
Unlike with a car, there's no
hard shoulder in the sky.

797
00:53:41,380 --> 00:53:43,700
'Creep can affect any metal.

798
00:53:43,700 --> 00:53:46,380
'In extreme environments,

799
00:53:46,380 --> 00:53:48,420
'the boundaries where crystals join

800
00:53:48,420 --> 00:53:53,220
'can become routes that atoms travel
along, elongating the crystals.'

801
00:53:55,180 --> 00:53:58,900
So, what can we do about creep?

802
00:53:58,900 --> 00:54:01,620
Metals are made of crystals,

803
00:54:01,620 --> 00:54:05,300
and if the crystal boundaries
are the problem,

804
00:54:05,300 --> 00:54:08,580
we can't take all the crystals out.

805
00:54:08,580 --> 00:54:10,660
Or can we?

806
00:54:14,660 --> 00:54:18,820
'This is the Rolls Royce
turbine blade facility, in Derby.

807
00:54:18,820 --> 00:54:22,500
'An entire factory dedicated
to making blades,

808
00:54:22,500 --> 00:54:25,580
'which work right at the heart
of a 21st century jet engine.

809
00:54:28,620 --> 00:54:31,260
'Here, they're actually
producing turbine blades

810
00:54:31,260 --> 00:54:34,580
'from a single metal crystal,

811
00:54:34,580 --> 00:54:36,620
'like a giant diamond of metal.

812
00:54:36,620 --> 00:54:39,580
'These blades are
resistant to creep.

813
00:54:42,660 --> 00:54:47,180
'Paul Withey is a casting specialist
at Rolls Royce.'

814
00:54:47,180 --> 00:54:49,900
This is where we cast
the single crystal turbine blades.

815
00:54:49,900 --> 00:54:51,580
This is the wax model of the blade.

816
00:54:51,580 --> 00:54:54,140
What actually do is,
as part of the assembly process,

817
00:54:54,140 --> 00:54:56,660
we'll fit in the spiral
onto the bottom of it,

818
00:54:56,660 --> 00:54:59,540
to allow us to grow a lot of
crystals in at the bottom.

819
00:54:59,540 --> 00:55:01,820
One crystal is selected
through a spiral,

820
00:55:01,820 --> 00:55:04,540
and made to grow through the whole
of the rest of the blade.

821
00:55:04,540 --> 00:55:07,820
'This is astonishing stuff.

822
00:55:07,820 --> 00:55:09,860
'We've conquered creep,

823
00:55:09,860 --> 00:55:12,860
'by growing our own metal.

824
00:55:12,860 --> 00:55:15,140
'The crystal boundaries
that cause creep

825
00:55:15,140 --> 00:55:17,660
'are prevented by the spiral tube,

826
00:55:17,660 --> 00:55:21,020
'which stops all but one
metal crystal getting through,

827
00:55:21,020 --> 00:55:26,340
'allowing that single crystal
to grow into the whole mould.'

828
00:55:26,340 --> 00:55:29,260
It's amazing that one of our
earliest activities with metal

829
00:55:29,260 --> 00:55:30,780
was to cast it.

830
00:55:30,780 --> 00:55:33,060
It's really where we came from,
as a civilisation.

831
00:55:33,060 --> 00:55:36,020
Here we are, one of the most
sophisticated pieces of metallurgy

832
00:55:36,020 --> 00:55:38,940
you can possibly do,
and it's casting again.

833
00:55:38,940 --> 00:55:42,340
Yes. And it's actually using the
same process that was used

834
00:55:42,340 --> 00:55:45,620
over 5,000 years ago, to make art
and religious artefacts,

835
00:55:45,620 --> 00:55:47,660
and here today is being used to make

836
00:55:47,660 --> 00:55:51,700
some of the most hi-tech engineering
components that you can find.

837
00:56:01,420 --> 00:56:03,700
'In this age of single crystal
turbine blades,

838
00:56:03,700 --> 00:56:06,940
'it seems that we've finally
understood how metals work,

839
00:56:06,940 --> 00:56:09,780
'and how to make them work for us.

840
00:56:11,820 --> 00:56:14,260
'Paul, and the engineers
at Rolls Royce,

841
00:56:14,260 --> 00:56:17,300
'are all upbeat about
the future of metals.

842
00:56:17,300 --> 00:56:19,340
'But not everybody agrees.

843
00:56:22,740 --> 00:56:25,620
'Some of my colleagues
in material science

844
00:56:25,620 --> 00:56:28,260
'are beginning to think
we've outgrown metals.

845
00:56:28,260 --> 00:56:29,820
'We've mastered them,

846
00:56:29,820 --> 00:56:32,500
'and now we should move on
to other materials.

847
00:56:32,500 --> 00:56:35,380
'But should we dismiss them
so easily?'

848
00:56:35,380 --> 00:56:38,020
Metals are in everything around us.

849
00:56:38,020 --> 00:56:41,060
The electricity that made
that kettle boil

850
00:56:41,060 --> 00:56:44,220
came down a wire, and that wire
itself is made of metal.

851
00:56:44,220 --> 00:56:45,700
Here's some.

852
00:56:45,700 --> 00:56:47,140
It's copper.

853
00:56:47,140 --> 00:56:50,540
So, the Copper Age is embedded
in our homes.

854
00:56:50,540 --> 00:56:52,620
It delivers all our
electricity to us.

855
00:56:52,620 --> 00:56:55,660
Then, the Bronze Age is still here,

856
00:56:55,660 --> 00:56:57,500
for anyone who likes sculpture.

857
00:56:57,500 --> 00:57:00,180
Beautiful, aesthetic material.

858
00:57:00,180 --> 00:57:03,420
The Iron Age is here,

859
00:57:03,420 --> 00:57:05,620
and steel?

860
00:57:05,620 --> 00:57:09,100
We spent thousands of years honing
this material to be strong, tough,

861
00:57:09,100 --> 00:57:11,260
and ultra-sharp.

862
00:57:11,260 --> 00:57:12,980
Let's not forget the modern metals.

863
00:57:12,980 --> 00:57:14,940
We fly around with aluminium,

864
00:57:14,940 --> 00:57:17,700
but it's in our kitchens, too,

865
00:57:17,700 --> 00:57:19,900
in this lovely, wafer-thin metal,

866
00:57:19,900 --> 00:57:23,580
which is just extraordinarily
versatile.

867
00:57:24,820 --> 00:57:27,940
But there's something a little sad
about the history of metals.

868
00:57:27,940 --> 00:57:30,020
Each one starts out
as a revolution.

869
00:57:30,020 --> 00:57:34,820
But, after a while, they recede,
and we take them for granted.

870
00:57:34,820 --> 00:57:37,300
But I really don't think we should.

871
00:57:37,300 --> 00:57:40,580
If it wasn't for metals,
we'd still be in the Stone Age.

872
00:57:40,580 --> 00:57:45,460
Everything around us is shaped
by metals. Everything.

873
00:57:45,460 --> 00:57:50,140
It's that step-by-step understanding
of the internal structure of metals,

874
00:57:50,140 --> 00:57:52,180
the secret world
of the metal crystal,

875
00:57:52,180 --> 00:57:54,820
that's been a huge
intellectual achievement.

876
00:57:54,820 --> 00:57:58,100
Metals have driven
civilisation forward.

877
00:57:58,100 --> 00:58:01,780
And, in doing so, they've defined
who we are as humans.

878
00:58:01,780 --> 00:58:04,940
And that's something
we should be VERY proud of.

879
00:58:26,900 --> 00:58:29,900
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