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ShareOct. 14, 2005 — It's one thing to imagine how an ancient technology worked and quite another to actually get your hands dirty trying it.
That's the whole idea behind "experimental archaeology" and the experiments Dan Jeffery is conducting with bloomery furnaces.
"Experimentation allows us to test theories about how we think technological processes worked in antiquity," said Jeffery, a Ph.D. student in Materials Science and Engineering. "And quite frequently experimental archaeology shows that the process didn't work the way we thought it did."
In this case, Jeffery is studying bloomery furnaces that were used to make iron and steel in Europe and the United States up until about 200 years ago. These furnaces also have a long history in many cultures, stretching back more than 2,000 years.
"Like a lot of ancient technologies, it gets treated as a simplistic technology," Jeffery said. "But attempts to recreate it have proven that it's not nearly as simple as people would like to believe. So far, we have conducted two separate smelts with bloomery furnaces and neither was terribly successful."
Iron from bloomery furnaces were used in Japan, Renaissance Europe, ancient Rome, Africa, and many other places to make iron and steel for armor, swords, locks, tools and hundreds of other household items.
"Iron has been a critical, fundamental part of human existence for centuries," Jeffery said. "Understanding how iron was produced and having a clear concept of what it took to do that and replicating that process today is significant from a scientific and human perspective."
How the Technology Works
Bloomery furnaces smelt iron in a direct reduction process, where the iron never becomes liquid. If the furnace gets too hot and the iron liquefies, it picks up a lot of carbon and becomes cast iron, which is too brittle to be worked into tools, swords and other objects that require a more flexible metal.
Most modern iron is produced by an indirect process in which cast iron is made first. Then the cast iron is heated a second time and the carbon is driven out.
"We're trying to quantify the operational characteristics of bloomery furnaces," Jeffery said. "It's an intriguing and really difficult task because there are many variables in air-flow design, charcoal used, furnace materials, the original source of iron ore and construction of the furnace."
The furnace produces a "bloom," which is like a big sponge, with a network of glass-filled channels running through it. The iron has loosely bonded together, leaving the glass that was produced from all the impurities in the iron ore.
Getting the right ratio of glass-to-iron is critical. If the original ore is too iron rich, the furnace won't produce the glass slag until the iron has been heated past its melting point, producing cast iron. If the furnace is too cool, or there isn't enough iron, the iron will act as a flux and the bloom will be mostly glass.
After the bloom is produced, a blacksmith starts working it while it is still hot, repeatedly hammering and reshaping it to drive the glass out, leaving the iron. With just a little manipulation, the iron is good enough for tools, although they might break easily where large glass inclusions make them weak. With lots of hammering, shaping and reheating, the blooms can be formed into the fine steel found in samurai swords, for instance.
Failure is Part of the Mix
Producing iron-rich blooms isn't easy. Even long-term smelting operations had failures, Jeffery noted. The ancient Romans, for instance, occasionally produced cast iron, which they considered worthless.
"We have some concept of what was done, but being able to do it successfully from a control perspective and yet still trying to use ancient materials is a little more challenging," Jeffery said.
The process started when Tom Mclane, a local blacksmith, pulled a magnet through Tucson washes to gather magnetite sand. Then Jeffery, Mclane and others heated the ore in the furnace with mesquite charcoal. The result was a bloom with very little iron.
Jeffery thinks the magnetite was too iron rich and dense. Most iron ores used in ancient European bloomery furnaces (the furnaces Jeffery is basing his work on) came from boggy environments and were very porous, unlike the dense magnetite.
Jeffery also plans to add some softer woods to the mesquite to modify the furnace temperature in future experiments.
"Iron often is referred to as the 'democratic metal' because it is so available," he said. "Whereas copper is much scarcer and wasn't distributed to everyone. Once technology for smelting iron caught on, everybody had access to metal."
So understanding how this metal was produced is critical to understanding the evolution of ancient cultures.
Getting in Touch With the Past
But even when such specific and important scientific questions aren't involved, Jeffery believes that duplicating ancient technologies can be important to understanding the past.
"We've involved a lot of people here in the materials science department who probably would never have had experience with an ancient technology and with grasping what is involved in doing this," Jeffery said. "Those students who came and saw the furnace in operation had a chance to work the bellows, see the fire, and feel the heat. They got some concept of how this was done and learned about one aspect of what helped us to be where we are today.
"So now they can relate to a piece of history in a way they would never have done if they had just read about it and not experienced it."
Jeffery has a bachelor's degree in linguistics and a master's degree in archaeological science. He came to UA's Materials Science and Engineering program because "I decided I wanted a much better, harder science background as I was proceeding down the archaeology road," he said.
Jeffery's research is part of UA's Heritage Conservation Science Program. Students in this program learn to stabilize, preserve and better understand ancient artifacts and how they were created and used.
The curriculum, which combines engineering, anthropology, architectural history and art history, is particularly important today because many of the material links to our past are disintegrating, while the ancient technologies that created them are disappearing.
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