A TIMELINE FOR THE PLANET click for Home Page
Metal working is one of the Great Inventions of
Mankind, like the wheel, writing
and, to my biased mind, the harnessing of steam.
The Copper age The Bronze age The Iron age
We’re talking work-a-day metals
here. To my mind, gold doesn’t count
because it’s too easy. Once you have
found your nuggets of gold, all you have to do is to melt them, and pour them
into a mould. I’m sure that’s not quite
fair, but the metals that actually transformed people’s lives are altogether
more difficult. Most metals are found in
the form of ‘oxides’ (rust). And they
have to be ‘smelted’ using charcoal, to drag the oxygen off. This is difficult, dangerous, and the fumes
that arise are not at all good for you.
Pure metals tend to be too soft to be of any practical
use. It’s when you add a suitable
leavening of other minerals (a few percent is enough) that they become hard
enough and tough enough to make tools, weapons or anything else. So don’t go asking for pure gold
jewellery. The stones would fall out,
the fixings would break and you wouldn’t keep it long. Much of the skill of the metal-master lies in
removing unwanted impurities, and in introducing the right concentrations of
the wanted ones.
I’m finding it extremely difficult
to give you any decent dates for the metals revolution. This perhaps adds weight to the theory that
it was ‘dark age’ peoples who had the freedom to innovate. Once a civilisation was established, its
elite saw change as a threat (more).
The first metal age was the copper age. Copper oxide is green, so it’s easy to
find. Today’s architects sometimes
sheath parts of their buildings in copper, and deliberately encourage it to
‘rust’ because they like the green colour.
The first smelters of copper seem to have been the
Anatolians (Turks), 8 or 9 thousand years ago.
Slag heaps have been found in the weird ‘stone age’ settlement of Çatalhöyük, showing that they were already into
copper smelting. But this doesn’t seem
to have been the start of any widespread copper age.
A better age for the start of the copper age seems to
be something over 5 thousand years ago.
You may remember Ötzi, the 5 thousand-year old mummified hunter who was
found in the high
The copper age doesn’t seem to have lasted very long
though. Indeed, not all authorities
accept that there was a separate copper age at all. Adding arsenic to copper may be good, but
adding tin to it is very much better.
This produces bronze. Some copper
deposits have tin already mixed in with them, so when you smelt them you get
bronze anyway.
The bronze age seems to have started during the ‘dark’
age preceding the Sumerians, which is to say
just over 5 thousand years ago. It
quickly spread around the
The discovery of bronze was the real breakthrough, and
it spawned a whole series of rich civilisations in the middle east and
elsewhere (see previous link).
These days we use an improved version of bronze,
adding zinc instead of tin, and call it brass.
But bronze is not terribly strong, and it can’t take a
truly hard edge for cutting. So there
was a need for a more durable metal still.
As far as I can gather the iron age began, again in the middle east,
around 3 thousand years ago, and reached
I’ve read that it was not any of the great
civilisations that discovered iron smelting either, but the Phoenicians, or
possibly the Samaritans.
Iron is funny stuff.
The main material you need to add to improve it is carbon – but only a
few percent. If you add just a little,
you get wrought iron. Wrought iron is a
very useful material. You can bend it
and stretch it, but it is still pretty strong.
If you add a little more carbon, you get steel. Steel is very hard and very strong. And it’s the material that props up most of
modern civilisation. But if you add a
little more carbon still, you don’t get better steel, you get cast iron. Cast iron is quite strong. The famous Iron Bridge is made of it. But it’s brittle. It won’t bend. It breaks instead.
Perhaps we should end with a brief mention of ‘the
steel age’. Steel has been around since
the middle ages. The Indians were
exporting quite a lot of it a thousand years ago. But steelmaking was a cottage industry. Steel was far too expensive to be used for
much, except swords. Only when Henry
Bessemer invented his famous ‘converter’ (see previous link), around 200 years
ago, did good steel become cheap enough to be widely used in industry.