Around 1200 BCE, a remote furnace in the hills of southern Georgia may have unwittingly ignited one of humanity’s most significant technological revolutions, paving the way for the Iron Age.
In a fascinating twist of ancient chemistry, copper-smelting artisans may have stumbled upon a technique that would eventually lead to the intentional extraction of iron from ore, a discovery that was both accidental and revolutionary.
A fresh analysis of slag, ores, and furnace residues from the 3,000-year-old site of Kvemo Bolnisi, Georgia, is rewriting the story of how humankind first learned to make iron.
A team of researchers from Cranfield University in England, reexamining old finds from Kvemo Bolnisi using modern techniques, suggests that what had once been labeled an early iron-smelting site was actually a copper workshop that utilized iron oxides as a flux.
The findings, recently published in the Journal of Archaeological Science, suggest smelters weren’t trying to produce iron at all, but were experimenting with iron-rich minerals to boost their copper yields. That experiment, researchers argue, may have been a crucial stepping-stone in the development of extractive iron metallurgy.
“Iron is the world’s quintessential industrial metal, but the lack of written records, iron’s tendency to rust, and a lack of research on iron production sites has made the search for its origins challenging. That’s what makes this site at Kvemo Bolnisi so exciting. It’s evidence of intentional use of iron in the copper smelting process,” lead author and visiting fellow in archaeological science at Cranfield University, Dr. Nathaniel Erb-Satullo, said in a press release. “That shows that these metalworkers understood iron oxide – the geological compounds that would eventually be used as ore for iron smelting – as a separate material and experimented with its properties within the furnace. Its use here suggests that this kind of experimentation by copper-workers was crucial to development of iron metallurgy.”
For decades, archaeologists have grappled with the mystery of how and exactly when human societies transitioned from Bronze Age copper-tin technology to Iron Age mastery.
Iron in metallic form is pervasive today. However, in antiquity, it was rare, and early iron artifacts are mostly meteoric, not derived from ore. The transition from working with copper and bronze to smelting iron ore required new chemical insights, new furnace management, and new raw materials.
The site at Kvemo Bolnisi was first excavated during the 1960s. Early archaeologists recorded significant stockpiles of hematite (an iron oxide) alongside smelting slags, which led them to conclude that this workshop had been an early iron smelter. However, this new reanalysis by Cranfield researchers throws that assumption into doubt.
By studying the microstructure of the slag and residual phases, the researchers demonstrate that the iron oxides behaved as a “flux,” a substance added to the smelting mix to help separate impurities and improve copper yield, rather than forming new iron metal.
In effect, the smelters were tinkering with iron-bearing minerals to optimize their copper output. However, that level of experimentation suggests a sophistication that may have seeded the later invention of iron smelting proper.
One of the main arguments of this new research is how it reframes ancient technological agency.
The metallurgists of Kvemo Bolnisi recognized that iron oxide was distinct and manipulable, and they tested it under furnace conditions. That act of “playing” with materials inside a furnace environment aligns with long-held theories that iron metallurgy was not born in a grand, instantaneous innovation. Instead, it emerged through iterative experiments within earlier metalworking traditions, specifically among copper smelters.
Instead of seeing copper and iron technologies as being sequential, the Cranfield study weaves them together. In that sense, the Iron Age might owe a kind of accidental debt to copper artisans who were seeking better yields, rather than a new metal.
Beyond its significance for metallurgy, the Kvemo Bolnisi work also poses broader questions about how human technologies evolve. It offers a concrete instance in which trial and error in one domain (copper smelting) incubated a significant leap in another (iron production).
The earliest known iron artifacts, nine beads from ancient Egypt dating to about 3200 BC, were not smelted from ore at all but hammered from meteoritic iron. The actual breakthrough came much later, with the leap to extractive metallurgy, which involved reducing iron directly from terrestrial ore, marking the true dawn of the Iron Age.
Yet, this new research affirms that the path to the Iron Age was neither swift nor uniform. Although many regions date its onset to around 1200 BCE, findings suggest it was the culmination of centuries of experimentation, which resulted in one of the most significant technological leaps in human history.
Because the original excavations lacked modern analytical precision, researchers first had to retrace the past. Using hand-drawn maps from the 1960s, they relocated the long-buried furnaces and slag heaps of Kvemo Bolnisi.
By reexamining the metallurgical waste from the site using modern microscopy, chemical mapping, and mineralogical analysis, the researchers were able to piece together critical clues, like furnace temperatures, redox conditions, and even the interactions of multiple mineral phases.
Despite the promising findings, the research team is cautious about drawing conclusions just yet and acknowledges that this is a reinterpretation of older material, and the absence of unequivocal early iron blooms at the site remains. Additionally, a single site cannot tell the whole story.
Researchers say that copper smelting sites elsewhere should be reexamined for similar traces. If Kvemo Bolnisi is not unique, then the narrative of iron’s emergence will need to shift. Rather than emerging from isolated innovators, iron may have emerged gradually from the practices of existing metalworkers.
Such a shift would have broader implications for how archaeologists think about innovation itself. Suppose multiple copper workshops across the ancient Near East were experimenting with iron-rich fluxes. In that case, the transition to true iron smelting may not have been a single eureka moment but a distributed process of trial, error, and incremental learning embedded in established craft traditions.
Ultimately, the rise of the Iron Age would look less like a sudden technological revolution and more like a slow-burning evolution, shaped as much by everyday metallurgical problem-solving as by isolated breakthroughs.
“Debates about the invention of iron will likely continue until we have accumulated more data on the geography, chronology, and technology of early iron smelting activities,” researchers conclude. “Encouragingly, research at Kvemo Bolnisi shows that the investigation of currently known sites has much to contribute to debates about the links between the bronze and iron technologies and their impact on iron innovation.”
“This work shows how the analysis of production remains not only reconstructs technological behaviors, it can also address questions of knowledge, perception, and intent.”
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com
