The ‘Second Industrial Revolution’: The Road to Architectural Steel, a History

Architectural Steel provides – almost literally – the building blocks of human civilisation. It has transformed how we live and operate as a species. But how did we get here? In this brief history, we’ve charted the course of humanity – from the beginnings of the Iron Age to the steel megaprojects of modern-day China.

A history of architectural steel.

1. The fundamental questions: What is architectural steel? What is metal?  

The late astronomer Carl Sagan once said: “We live in a society exquisitely dependent on science and technology, in which hardly anyone knows anything about science and technology.”

A simple test of this theory is to ask someone what architectural steel is. They might mention something like, “it’s what they use to build buildings”. But apart from that, the general public has no clue. It’s an astonishing realisation, that most of us have no clue what it is.

            Metal is a chemical

At the most basic level, metal is a chemical substance. Metals are commonly found all over the Earth. Over millions (or even billions) of years, geological forces can fuse these minerals together in large quantities in a rock. This process, known as ore genesis, gives birth to ores.

What is ‘ore’?
The word ‘ore’ is just a general term for any rock containing a sufficient concentration of metal for it to be extracted economically. Most ores result from volcanic activity. Magma under the Earth can force minerals and metals such as iron together in large concentrations. A good example is the 200-km-wide Bushveld Complex in Johannesburg, South Africa, which contains enormous amounts or iron, platinum and gold. Steel is made from one metal, iron.

A piece of iron consists of millions of small crystal grains, all packed together. Iron is abundant and cheap, and by mass is the most common element on Earth. Much of the Earth’s inner and outer core is made of iron. It is also common throughout the Universe. So if iron ore is less than 50 per cent iron, it is usually not usually worth extracting.

            Steel is a blend of iron and carbon atoms

Add carbon to a metal and it changes the metal’s properties substantially. And by controlling how much carbon is added, the strength and hardness of the metal can also be manipulated. When a metal is combined with another metal, or a non-metal, this combination is called an alloy.

2. Before architectural steel: material revolutions

The road to architectural steel is one spanning millennia, and involving all of humanity. In order to appreciate this journey, let’s take a moment to consider the building blocks that came before it:

A wooden building.


Before architectural steel, there was wood. And timber is one of the most ancient building materials. For millennia, humans have used timber for beams, planks, and poles for construction.

Before architectural steel, wood was very useful. Elm wood is very tough and rarely splits, making it ideal for cartwheels. Hickory wood – being especially hard – was suitable for the gear teeth in the power mechanisms of windmills and watermills. The tall and straight trunks of pine and fir trees made perfect masts for ships.

Clay buildings in Morocco


Before architectural steel, there was clay. Today, when we think of clay, we think of pottery – maybe even art class. But clay was an early building material, ever since clay blocks were first fired up into clay bricks. The image above shows a narrow, North African street with clay facades on all of the buildings.

Clay beds are widespread throughout the world, and in some cases, even lie above the soil. Clay is made out of very fine sheets of aluminium and silicon. Rocks erode over time, releasing aluminosilicate minerals. These minerals are then transported by rivers until they are deposited, forming a clay bed.

Fired up to around 300 – 800 degrees Celsius, clay becomes drained of all water. This creates very durable ceramic clay.

Fired clay was useful to society because it is hard and watertight. The aluminosilicate also has an extremely high melting point. Ceramic clay has probably been around longer than you think. The earliest example is about 30,000 years old.

Colosseum made from Roman concrete


It was the Romans who invented concrete. They did so by mixing slaked lime (limestone, combined with water and other materials) with volcanic ash and pottery. It enabled the Romans to build the wonderful architecture of their empire – including the roof of the Pantheon in Rome, the largest single-piece concrete dome in the world and the famous Colosseum or ‘Flavian Amphitheatre’ in Rome (pictured above).

Volcanic ash and clay both contain aluminosilicate, which is partly the reason why they make such strong substances. But when aluminosilicate chemically reacts with slaked lime things get really tough. The Romans were now able to lead the charge in architectural development. Concrete even set under water. The Romans built lighthouse foundations, quays, sea walls, harbours and fortresses with it.

This Roman invention was almost lost to history after the collapse of the Empire, surviving in tiny projects across Europe. It wasn’t until 1794 when ‘modern’ cement was invented. ‘Portland cement’ has a simple recipe (with a few minerals for seasoning):

Limestone + clay + sand + water

Cement sections – a bit like the sections and structures and plates we associate with architectural steel – were sculpted from pouring cement into a wooden shuttering and waiting for it to settle.

3. The metal renaissance

After the Second World War left much of Europe in ruins, concrete led the charge in the rapid rebuilding of society. This was mostly because it is cheap, strong, and easy to make – a quick fix. Historically, though, concrete has left architects wanting. Sure, it’s very strong when compressed in foundations and columns, but it’s very weak under tension.

Unlike wood centuries earlier, concrete does not allow for the building of large structural elements like beams, bridges, or the floors of multi-storey buildings. Try to build a beam out of concrete, and it will crack catastrophically. The beautiful architecture associated with steel – and even wood – is not possible with concrete.

            Reinforced concrete

The earliest recorded attempt to circle around concrete’s weakness was in 1853, by a plasterer. The plaster used his initiative and straightened some metal battle hoops into concrete floor slabs as they were hardening.

It worked like a charm. It became common to embed steel rods into concrete. The properties of both materials work very well together: combining the compressive strength of concrete with the tensile strength of steel. This image (below) shows a steel reinforcement bar with a wet concrete covering.

Wet concrete poured on a steel reinforcement bar.

            Exploiting steel for architecture

Steel is made from carbon and one metal, iron. Throughout the history of civilization, iron has been exploited because it changes its physical properties when hot. Heat iron up enough and it can be softened to a malleable point. Hot iron can be beaten into shape, made into sheets, and rolled into pipes and wires.

Why is architectural steel so tough?
Architectural steel is strengthened by heating it until it is red hot. The process is known as tempering. At such high temperatures the internal structures of steel’s iron-carbon crystals convert into a rigid conformation. But if allowed to cool slowly, these crystal formations can revert back to a soft position.
To stop this from happening, metalworkers undertake a process known as quenching. The idea is to chill the steel rapidly, to freeze the crystal structure into place, by dunking the steel into water or oil. Quenching steel can make it very hard but also brittle – meaning the steel could shatter without further tempering. So metalworkers reheat the steel again, to a lower temperature than before to unlock some of the crystal structures. This makes the steel less hard, but also less brittle. Metalworkers can fine-tune architectural steel for many uses and purposes by tempering steel like this.

This created a positive feedback loop. It allowed metalworkers to make iron tools, to then work on more iron and produce even better iron tools.


Welding is the practice of gluing metal together with molten metal. Without welding, architectural steel would not exist. The building blocks of civilization are made from steel – and superhot metal is the glue that holds civilization together.

The hottest flame of any fuel gas is Acetylene. Acetylene yields over 3,200 degrees Celsius when it is burned in a stream of oxygen. Welding is a relatively recent technology, coming about in the 19th Century. The Englishman Edmund Davy is credited with the discovery of Acetylene in 1836, but a suitable torch for making use of Acetylene was not invented till about 1900.

A welding torch requires a separately controlled pressurized flow of oxygen and Acetylene gas through a lit nozzle. The modern process of welding, known as the oxyacetylene process, was commonplace by about 1916.

How was the welding torch invented?
To create a welding torch, we need two separate ingredients: pure oxygen and Acetylene gas. Two common processes to create pure oxygen include the electrolysis of water, and the distillation of liquefied air. Acetylene gas is released as water reacts with calcium carbide. Calcium carbide itself is made by heating quicklime and charcoal together in a furnace.

The welding torch is not just essential for gluing architectural steel together. The oxyacetylene flame also makes a brilliant cutting torch. With it, metalworkers can streamline a jet of combusting oxygen into a hypothetical ‘blade’, and slice hot metal into neat lines. Welding as a process gives metalworkers what they need to refine, shape, and put together the architectural steel that makes up our world. There are even more powerful tools at our disposal. Electric arc welders generate temperatures of around 6,000 degrees Celsius – hotter than the surface of the Sun.

            Recycling architectural steel

Electric arc welders are used to melt down scrap metal for recycling purposes in electric arc furnaces. These technological marvels essentially harness the power of lightning.

How do electric arc welders work?
Electric arc welders are important for recycling architectural steel because of the high temperatures they reach. An electric arc is the result of gas that is broken down to a point where it releases electrical discharge. A carbon electrode is a conductor. A conductor allows electricity to pass easily through it. It allows the electricity to jump back-and-forth, to weld or cut as the electrode is moved over the target metal.

In an electric arc furnace, large carbon electrodes surge electricity through the metal to melt it, with a limestone flux used to remove impurities such as slag. In such furnaces, molten steel runs like water from a boiled kettle.

The ability to breakdown and recycle steel in this way is why steel is classed as a sustainable architectural material – the most recycled material on Earth. Steel does not degrade in performance, no matter how many times it is recycled. About 86 per cent of the world’s steel is re-used over and over in a continual recyclable loop.

4. Making architectural steel

The fruit of architectural steel lies, humbly, in the Earth itself. In order to even think about building anything out of steel, iron ore must be found.

Iron ore is common on Earth. So much so, that it isn’t worth extracting if the ore isn’t at least 50 per cent iron.

Iron ore extraction can be as simple as a good pair of eyes and a pickaxe if the ore is exposed enough – although this form of extraction is no longer common. The modern world’s insatiable thirst for architectural steel requires increasingly sophisticated methods.

            Finding architectural steel

Today, geologists use satellite data, airborne surveys, and infrared light to locate ‘surface effects’ that indicate where large concentrations of iron ore may be.

Other exploration techniques include mapping the magnetic field and looking for anomalies. Metals – of which iron is a metal – distort the magnetic field, allowing geologists to zone in on potential ore deposits.

When an ore deposit is found, it must be drilled to assess the quality of the ore and how big the deposit is. Drilling is very expensive and is usually the last stage of exploration for any buried ores – and even then, only about 1 in 1,000 promising-looking ore deposits has everything needed to turn it into a successful mining operation.

Most of the iron found today comes from banded iron formations (BIFs). BIFs are thought to have formed about 2 billion years ago, during a time in Earth’s history where oxygen wasn’t all that common and bonded with iron to form insoluble oxides. Famous examples of BIFs include the Lake Superior district in the United States and the Hamersley Basin in Australia. In both places, iron is extracted in huge pits and has been since the nineteenth century.

Below is an image of a digger extracting iron ore and loading it on to a train. The train will then take the ore to a factory, where it can be smelted.

A digger loading iron ore on to a train.

Did you know?
Raw iron also arrives on the surface of Earth in meteorites, which is why the ancient Sumerians called it the ‘metal from Heaven’. The Indians of North America used only iron from meteorites, because they did not know how to smelt it from the iron ore already on Earth.

            Extracting architectural steel (smelting)

Architectural steel is made from iron, and iron is found in iron ore in the Earth. To get the iron successfully out of the ore, so that it can be used in architectural steel, we need to use a process called smelting.

The general principle of smelting is to remove any oxygen, sulphur, and other elements that the metal is combined with in its ore. To do this, high temperatures are needed. In fact, three things are needed:

A high temperature + a reducing agent + a flux

This is not as difficult as it sounds. Charcoal burns high enough to qualify for the smelting temperatures needed. It also releases carbon monoxide as it combusts. Carbon monoxide is a powerful reducing agent.

What is a reducing agent?
A reducing agent is a substance that steals oxygen, and hoards it all to itself. Once it has finished ‘stealing’, we say that it is oxidised. In the smelting process, it is necessary to free the metal from any oxygen it is bonded with. A reducing agent does this by stripping the oxygen away and leaving behind pure metal.

A typical iron-smelting furnace has layers of charcoal fuel for exactly this reason. In such a furnace, the charcoal is mixed in with the crumbled up iron ore rock. In this mixture, the flux is then added.

A flux is a ‘cleaning agent’ in chemistry. It washes away impurities. In this iron-smelting furnace, limestone serves as the flux. The limestone works by lowering the melting point of all the useless bits of the ore rock. It turns the useless bits into a liquid, and washes everything that isn’t pure iron away.

This waste, drained away from the furnace, is called slag. Once the slag is drained away, all that remains behind in the smelting furnace is the iron, waiting to be extracted.

Did you know?
Smelting is a millennia old process. The ancient Cypriots smelted copper ore as long ago as 4,000 BC. We know this by observing the huge piles of ancient slag still in Cyprus to this day. It is estimated that all of the forests of Cyprus must have been felled many times to feed the copper industry. The process relied on the Cypriot climate favouring rapid timber regrowth.

This is what a blast furnace, or iron-smelting furnace looks like on the inside:

Making architectural steel, a blast furnace

            Making architectural steel

It wasn’t always easy to operate a furnace at a high enough temperature to melt iron. In such cases, the ancient Chinese and the mediaeval Europeans would be left with a spongy lump of impure iron.

In such cases, these early metalworkers would have to pummel the iron on an anvil. By pummeling the spongy iron, the remaining slag is squeezed out, and the iron fused closer together. Iron in this state is known as wrought iron. Wrought iron sometimes has distinctive filaments where the slag has not removed completely.

You may be familiar with the concept of mediaeval steelmaking from popular culture. Here is a blacksmith forging iron on an anvil:

A blacksmith forging iron on an anvil.

Did you know?
The European knights of the realm crafted their swords of steel in blast furnaces. To get the steel they needed wrought iron. Wrought iron is a tough, malleable form of iron suitable for forging and rolling. To make it steel, wrought iron has to be heated a second time, with charcoal for the iron to absorb carbon, and then pummeled on the anvil again.

Steelmaking in the pre-modern era was backbreaking and not very productive. Steelmakers would repeatedly have to batter wrought iron: folding, bending, and re-positioning and reheating it to make uniform steel.

            Making industrial architectural steel

Wherever the blast furnace was introduced in the world, it quickly became very popular. The earliest known use of the blast furnace dates to around 500 BC, in ancient China. A whopping 1,500 years before it first appeared in Europe.

A blast furnace works by forcing a powerful stream of air up to the top of the furnace stack to really intensify combustion. The Chinese improved on their designs as the Europeans continued to pummel anvils, by introducing bellows that pumped in hot air. These bellows acted like pistons, and were powered by waterwheel technology. Temperatures rose even higher, as waste heat was trapped and recycled to pre-heat the hot air even more.

Iron more readily absorbs carbon in a blast furnace, which acts to lower its melting point to about 1,200 degrees Celsius. Instead of a spongy, half-cooked wrought iron, the iron in a blast furnace turns into liquid. In the earliest European blast furnaces, the liquid iron drained out of the bottom of the furnace, where it pooled in ingot moulds.

Anyone who has seen a cartoon bar of gold will be familiar with the shape of an ingot mould (see the image below). An ingot mould is an ideal shape for further metallurgic processing, as it helps with cooling and to prevent cracks appearing. The Europeans thought the cooled iron in the ingot mould resembled newborn piglets suckling on a sow. For that reason alone, iron processed in this way is known as pig iron.

Ingot moulds of gold and pig iron.

With the development of pig iron, our world took its first baby steps into the age of architectural steel. Pig iron is naturally high in carbon, which reduces its melting point. It can be re-melted and poured into casts like a hot wax. This is called cast iron. Cast iron was hungrily adopted by the Victorians, who at the height of the British Empire had grand architectural designs – much as the Romans had thousands of years earlier.

Here are just some of the fabrications the Victorians readily made out of cast iron:

  • Cooking pots
  • Pipes
  • Machinery parts
  • Cast iron girders

Great engineering projects and buildings were sculpted from cast iron. Unfortunately, cast iron has weaknesses not unlike concrete. The high amounts of carbon make it brittle under stress. A cast iron bridge, for example, will collapse if its structural components are bent or stretched too much.

Solving the cast iron problem ushered humanity into the full-blown age of architectural steel.

            Global hegemony: the age of architectural steel

Too much carbon makes iron brittle. Cast iron is typically about 3 – 4 per cent carbon. This may not sound like a lot, but architectural steel is generally around 0.2 per cent carbon. This gives it the strength it needs to be for machine gears and magnificent structural projects.

Did you know?
Different types of steel have more carbon than others. Steel of about 1.2 per cent carbon content makes for pretty hard ball bearings and for the steel found in cutting tools. What makes ‘steel’ is generally the range between pure wrought iron and brittle pig iron.

Ask a person on the street what a Bessemer converter is and they likely won’t have a clue. This is a shame, because the Bessemer converter is radically transformed almost every aspect of our daily lives.

The Bessemer converter was invented in the later stages of the Industrial Revolution, by a man named Henry Bessemer, in England. It has a distinctive shape, looking like a giant pear-shaped bucket. Newer technology has made the Bessemer obsolete. The ones still around today are antiques (see below):

A Bessemer Converter.

A Bessemer converter is charged with molten pig iron, and air is pumped up through the bottom. The carbon reacts with the oxygen and escapes as carbon dioxide gas. Other impurities are also oxidised and scrubbed out into the slag. As the carbon burns, it releases enough heat to keep the iron in liquid form throughout.

The Bessemer converter was the first method in history for cheaply mass-producing steel.  It allowed for just the right amount of steel to be manufactured. For just the right amount of carbon to be contained in or released from iron.

The Bessemer converter ushered in the steel age. Some call this the Second Industrial Revolution.

5. Apex: Architectural Steel today and Beyond

Today’s steelmaking has improved a lot since the Industrial Revolution, but it is still based on the same premise as the original Bessemer converter process. In fact, more than 70 per cent of all steel produced is still made in the blast furnace. But here are some ways that architectural steel has changed:

            Hybrid steels

One of the great discoveries of human civilisation is that pure metal is weak: it is actually the impurities that make it stronger, hence why iron is so much stronger when alloyed with carbon (to make steel).

One example of the ‘new’ steels is low alloy steel. This alloy may have impurities of up to 10 per cent including molybdenum, manganese, nickel, and so on. Low alloy steel is engineered to make thick sections of steel even harder.

One of the most famous hybrids is stainless steel. In some cases, it is up to 30 per cent chromium in impurity. It is the chromium that makes the steel so resistant to corrosion and to heat. Hybrid steels can be tweaked and engineered to suit their surroundings. There are more than 100 types of stainless steel in the world today – all crafted by imparted wisdom, artisanship, and knowledge over the centuries. Tailor-engineered steel is what gives today’s and tomorrow’s architect’s grander visions and greater dreams.

            New technologies

Over a century of progress has spawned an entire race of metal fabrication machines. Some of the most precise, and most efficient, include computer-controlled ring rollers, CNC plasma tables, and Tekla computer software. Read more about them here.

            Steel-making is greener than it ever has been

The Industrial Revolution is often pictures as a multitude of chimney stacks belching clouds of carbon. Today, steel is one of the most recycled and sustainable materials on the planet.

In many cases, the most important source of steel actually comes from recycling. This is much cheaper than drilling for iron ore deposits in the Earth, and there is so much steel that has already been mined. About 1 billion tonnes of steel will be available for recycling in 2030.

Because steel can be superheated and poured into a cast, it can be recycled again and again. The drive towards a more sustainable steel future has also seen a shift away from using coke to produce heat. Now, instead of coke, electricity is used. Electric arc furnaces are greener, cheaper, and less demanding energy-wise to run.

Since 1960, the steel industry has decreased its energy consumption (per tonne of steel produced) by 60 per cent.

            Steel-making is truly worldwide

The steel industry, in its modern form, was born in Europe and the West in the mid-to-late nineteenth century. The technology rapidly spread around the world, where it was enthusiastically adopted by the developing Far East.

Today, the balance of power has shifted from West to East. China alone produces half of all global steel production, with the United States lagging behind Japan and India. China, a country of over a billion people that’s rapidly getting richer, needs steel infrastructure to enable its citizens to travel over the country, either to work or on holiday. It has just finished building the world’s biggest sea bridge, including underwater tunnels and artificial islands, using enough steel to build 60 Eiffel towers in the process.

Conclusion: The invention of architectural steel, the greatest story never told

Going back to the Introduction, it is our opinion that the story of architectural steel is one of the most underappreciated triumphs of human history. Most of the population doesn’t even know what steel is, and that is a great shame.

From humble beginnings, at the depths of the Earth or from outer space, the base metal for steel, iron, has been collected, smelted, and hammered into tools and building materials for centuries. We are largely ignorant today, as we attend new football stadiums, drive over magnificent new bridges, of the natural, raw power of nature.

It’s time to talk about humankind’s greatest story, and this is what we hope we have achieved here, to some degree or another.

At Weldwide, we are architectural and structural metal workers. If you have a project in mind we can help you with the design, manufacture, and installation of a metalwork fabrication. From staircases to railings, structures, and beyond using the latest technology. Visit our home page here, and don’t forget to contact us if you have any questions.



Rothery, D. (2015) Geology: A Complete Introduction. London: Hodder Education, An Hachette UK Company

Bronowski, J. (2011) The Ascent of Man. Great Britain: BBC Books, Ebury Publishing

Dartnell, L. (2014) The Knowledge: How to Rebuild Our World from Scratch. London: Vintage Books

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