Iron and Its Place in the Ancient World
By Alchemist-hp (www.pse-mendelejew.de) - Own work, FAL, https://commons.wikimedia.org/w/index.php?curid=10115787
Iron is the 26th element on the periodic table and by mass, the most common element found on Earth with most of it being locked away within the core, leaving it the fourth most common element in the crust. In it's pure form, which rarely occurs on the surface, unlike like gold, silver, and copper do, it is a silvery-gray metal that reacts readily with water and oxygen forming a brown to black iron oxide, more commonly known as 'rust'. Rust takes up more space than the original iron does, which exposes more of the iron to the oxygen or water as it flakes off. There are four stable isotopes, though iron-56 is the overwhelming majority of iron on earth at 91.754%. The other isotopes are iron-54, which is 5.845%, iron-57, 2.119%, and iron-58, 0.282%. Iron synthesis triggers stellar supernovas known as type II supernovae, where the core collapses because producing iron doesn't produce any energy to keep the star from collapsing. As the star collapses, it rebounds off its core and explodes. It is also formed in type Ia supernovae which are caused by material falling on a white dwarf star usually from a companion star, appearing in the cloud of material around the explosion site after some time has passed as radioactive products decay. Iron is also the end result of radioactive decay because it takes energy to split iron atoms as opposed to releasing energy. When unalloyed iron is found on the surface, it is most likely from meteorites, which are remnants of the cloud of material that the solar system form from, indicating that there was most likely a supernova in the vicinity where the sun formed. Iron is required by every form of known life on earth In microbes, it is used in proteins that are used in transporting oxygen and for nitrogen fixing.
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Meteoric iron usage goes back as far as the 4000 BCE in Egypt and Sumer where the iron was made into ornaments or spear tips. It's likely that, because of its rarity in this form, iron was worth more than gold. Records show that the Hittites bartered iron for 40 times its weight in silver by the first centuries of the 2nd millennium BCE. These meteoric iron tools were also found in the Arctic, where pea-sized bits of iron were hammered into disks that were then fit into bone handles. These were used as trade, with some tools made from a meteor found in Cape York, Greenland, known as the Innaanganeq meteorite, which is one of the largest known meteorites in the world. These were traded for other goods, with some of the tools made from the Innaanganeg meteorite found 1600 km away from the meteorite.
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It's unclear exactly where iron smelting, or the extraction of iron from oxidized iron ores, began. Smelting iron is more complicated than smelting tin or copper, which require only relatively simple furnaces, like the kilns used for pottery, to produce melted metal. Iron smelting requires furnaces that reach higher temperatures and was quite often used as a flux, or a material that helps purge impurities from the desired result, in copper smelting which made it 'not surprising that humans mastered the technology of smelting iron only after several millennia of bronze metallurgy'. The beginning of iron smelting as it is difficult 'distinguishing metal extracted from nickel-containing ores from hot-worked meteoritic iron' which began in the 3rd millennium BCE, but worked iron artifacts are rare until the 12th century BCE.
By Giovanni Dall'Orto. - Own work, Attribution, https://commons.wikimedia.org/w/index.php?curid=15648126
The Iron Age is defined by the 'replacement of bronze weapons and tools with those of iron and steel', which happened in various locations at different times. Around 1500 BCE, non-meteoritic iron began to outnumber those created from meteorites. Iron was smelted in furnaces that had air forced through iron ore and burning charcoal by bellows, a structure known as a bloomery. This resulted in a spongy mass known bloom that would then be beaten to force out the by products, or slag, resulting in wrought iron, which is a relatively soft alloy of iron and carbon, making it a 'mild' steel. At some point, during the transition from bronze tools to iron, iron workers found they could improve the strength of iron by heating it over charcoal once the piece is finished and then quenching, or rapidly cooling it, in water or oil, which would turn the outer layers into a higher grade of steel and made the core less brittle than it was before.
It used to be thought that this process was developed by the Hittites and spread to other groups after the Sea Peoples destroyed their empire, it spread through the region, but there is no evidence to support this theory in the archaeological record. More recent theories suggest that the disruption of copper and tin trade during the Late Bronze Age Collapse, causing smiths to turn to iron. This, too, lacks archaeological support as bronze items remained abundant.
By Photograph taken by Mark A. Wilson (Department of Geology, The College of Wooster). - Original photograph, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4150061
In India, iron smelting likely began in India during the 2nd millennium BCE at places like Gangetic plains along the northern border of the Indian subcontinent, where it appeared between 1800-1200 BCE. Iron smelting was practiced in a large scale by the 13th century BCE, reaching southern India by between the 12th and 11th centuries BCE. Iron was used for a broad range of applications, from knives and other types of blades to bowls and spoons to door fittings by around 600 BCE. By 500 BCE, high quality steel began to be produced by the crucible technique, where iron ore and potentially lower grade steel, are put into a crucible, a container that is able to deal with very high temperatures, along with various fluxes, like sand, glass, or charcoal. Wootz steel, which is a very high-carbon crucible steel known for its strength, was developed in Sri Lanka around 300 BCE and would be prized through Classical Antiquity through the Middle East and Mediterranean world. Sri Lanka made use of the monsoon winds to fire their furnaces. This would cause a pressure difference in the kiln that led to higher temperatures and better quality steel. An iron pillar was erected between about 375-415 CE in modern day Delhi still stands today with very little corrosion despite being nearly pure iron and being exposed to heavy rains.
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In China, the oldest known iron artifacts date to the 14th century BCE and are from the Siwa culture in the modern day Gansu Province, likely from the Afanasievo culture that lived in southern Siberia. China developed bloomeries around the 9th century BCE in the central plains. The workers in southern Wu developed furnaces that reached temperatures of 1130°C, which is where 'iron combines with 4.3% carbon and melts', creating a better grade of steel than bloomeries, one that is less laborious to work with than the metal from bloomeries. Around 300 BCE, the process of decarburization, or reducing the carbon content of 'wrought iron by heating it in air for several days', resulting in a less brittle material, made iron the tool of choice through the area. The Han dynasty made ironworking a state monopoly, though this was eventually repealed. Blast furnaces were then built in Henan province, each capable of producing several tons per day. In the 1st century BCE, it was discovered that mixing wrought iron and cast iron, which have different iron contents, together resulted in an steel with a medial amount of carbon, attributed to Liu Bang, the first Han emperor, in legends because of texts mentioning 'harmonizing the hard and the soft' when talking about ironworking. The Han dynasty is when the waterwheel was applied to powering the bellows of blast furnaces, in about 31 CE, when it was recorded by Du Shi, who was then the Prefect of Nanyang.
