The whole reason that time period was named as such was because iron was the strongest metal that anyone had at the time, and whoever had the most advanced metal would have a decisive edge over their opponents. Iron is considerably stronger than bronze, the main metal of the preceding age and although it was good enough to make weapons and tools out of, they were not strong enough to make contraptions such as the plough.
The reason no one discovered how to make iron was because no one knew how to melt it. Iron ore was indeed found but when placed in a roaring fire it would not melt like copper and tin did, and so it was considered a useless chunk of rock. Iron’s melting point is 1,538 °C, way to hot to reach in any wood burning fire, but with the invention of the bellows and the addition of coal, this previously useless rock now turned into a source of a metal stronger than any other before it.
Step one – Locating ore
Bronze tools would be capable of mining rock, but it would take a huge amount of them as they’d blunt to quickly and would make the cost of doing so not worth the reward. However iron ore is quite common and as long as its starved of oxygen and water, it wont rust.
If you ever see a stream with a red coloured sand like substance on the bottom, then that indicated there’s iron nearby that has partially rusted and run into the water supply. Bogs and swamps would be a good place to get some starter ore, as you could simply dig down and find chucks of ore that the thick mud has protected from the water and air. After the initial batch of iron was found and smelted, mining tools would be the first thing to make as iron ore isn’t exactly rare and much more effectively taken from rock instead of swamps.
Step 2 – The smelter
The denser an object the better it can hold heat, and so a rock smelter would have been built using rocks stacked with a clay and sand mixture to stick them together. Later they would have been made using mortar instead of clay and also greatly increased in size, but initially smelters would have started out quite small.
Step 3 – Primary Smelt
In order to reach the required heat of 1,538 °C, a bellows would be used to constantly blow air into the smelter to increase the temperature, it would also be layered alternatively with coal and iron ore. When the temperature was hot enough the iron would melt and start to run out of the ore. This first casting of iron is known as pig iron and contains a very high carbon content, something it gained from the other minerals in the rock burning up and running out with the iron.
Pig iron is very brittle and would shatter if struck hard enough, its so weak that if you had a table knife made from pig iron, you could snap it in half with your hands no problem. The reason its called pig iron is due to the layout drawn in the earth to collect the melted iron. A line is drawn in the ground from inside the smelter that leads outside were it has rectangle run-offs either side of it, sort of like a collection of suckling pigs either side of their mother.
Step 4 – Secondary Smelt
Since pig iron is pretty much useless, it has to be processed again in order to be useful. The second smelting process would be the same as the first, but this time there wouldn’t be all that rock ore inside to burn off and add impurities. Smelting a second time didn’t exactly clean the iron perfectly but it did remove enough of the carbon content to make the iron strong enough for tools and weapons.
Step 5 – Forging
At this stage if you melted your iron down and poured it into a mould, you would have cast iron. It is strong enough to make things like pots and basic knives, but it will shatter if hit hard enough, making it useless for swords and heavy wear tools like the plough.
(Blacksmiths at a settlement could get away with using as little as a bellows to heat their coal fire, and nothing more than a hammer and anvil, or anvil substitue like a solid flat rock)
When iron is heated and compressed the bonds between the iron molecules become closer together and increase in strength. Simply getting the metal red hot and smashing it with a hammer over and over will make it strong enough to make the harder tools, and when people realised this it gave birth the large scale mining operations. Hacking ore out of rock and smelting it at the mine site was the most efficient way to distribute it, sending out bars or blocks of metal direct from the mine to settlements would mean they only need their own blacksmiths forge instead of building huge smelters all over the place.
The iron age ended in Britain in 45 AD when the Romans invaded the country and with them bringing the technology to make steel. The iron age ended at various times depending on where you are in the world and the conditions of the time, for example the iron age ended in Scotland more than 200 years after it did in England as the Romans couldn’t conquer the Scots, which meant they didn’t share their steel making technology with them.