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Making Iron The Old-Fashioned Way Is A Tricky Business

Date:
October 14, 2005
Source:
University Of Arizona
Summary:
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. 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.

Dan Jeffery adjusts his bloomery furnace during an experiment to produce iron using an ancient technology.
Credit: Image courtesy of University Of Arizona

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 thinktechnological processes worked in antiquity," said Jeffery, a Ph.D.student in Materials Science and Engineering. "And quite frequentlyexperimental archaeology shows that the process didn't work the way wethought it did."

In this case, Jeffery is studying bloomery furnaces that were usedto make iron and steel in Europe and the United States up until about200 years ago. These furnaces also have a long history in manycultures, stretching back more than 2,000 years.

"Like a lot of ancient technologies, it gets treated as a simplistictechnology," Jeffery said. "But attempts to recreate it have proventhat it's not nearly as simple as people would like to believe. So far,we have conducted two separate smelts with bloomery furnaces andneither 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 forarmor, swords, locks, tools and hundreds of other household items.

"Iron has been a critical, fundamental part of human existence forcenturies," Jeffery said. "Understanding how iron was produced andhaving a clear concept of what it took to do that and replicating thatprocess today is significant from a scientific and human perspective."

How the Technology Works

Bloomery furnaces smelt iron in a direct reduction process, wherethe iron never becomes liquid. If the furnace gets too hot and the ironliquefies, it picks up a lot of carbon and becomes cast iron, which istoo brittle to be worked into tools, swords and other objects thatrequire a more flexible metal.

Most modern iron is produced by an indirect process in which castiron is made first. Then the cast iron is heated a second time and thecarbon is driven out.

"We're trying to quantify the operational characteristics ofbloomery furnaces," Jeffery said. "It's an intriguing and reallydifficult task because there are many variables in air-flow design,charcoal used, furnace materials, the original source of iron ore andconstruction of the furnace."

The furnace produces a "bloom," which is like a big sponge, with anetwork of glass-filled channels running through it. The iron hasloosely bonded together, leaving the glass that was produced from allthe impurities in the iron ore.

Getting the right ratio of glass-to-iron is critical. If theoriginal ore is too iron rich, the furnace won't produce the glass slaguntil the iron has been heated past its melting point, producing castiron. If the furnace is too cool, or there isn't enough iron, the ironwill act as a flux and the bloom will be mostly glass.

After the bloom is produced, a blacksmith starts working it while itis still hot, repeatedly hammering and reshaping it to drive the glassout, leaving the iron. With just a little manipulation, the iron isgood enough for tools, although they might break easily where largeglass inclusions make them weak. With lots of hammering, shaping andreheating, the blooms can be formed into the fine steel found insamurai swords, for instance.

Failure is Part of the Mix

Producing iron-rich blooms isn't easy. Even long-term smeltingoperations had failures, Jeffery noted. The ancient Romans, forinstance, occasionally produced cast iron, which they consideredworthless.

"We have some concept of what was done, but being able to do itsuccessfully from a control perspective and yet still trying to useancient materials is a little more challenging," Jeffery said.

The process started when Tom Mclane, a local blacksmith, pulled amagnet 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 ironores used in ancient European bloomery furnaces (the furnaces Jefferyis basing his work on) came from boggy environments and were veryporous, 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 isso available," he said. "Whereas copper is much scarcer and wasn'tdistributed 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 questionsaren't involved, Jeffery believes that duplicating ancient technologiescan be important to understanding the past.

"We've involved a lot of people here in the materials sciencedepartment who probably would never have had experience with an ancienttechnology and with grasping what is involved in doing this," Jefferysaid. "Those students who came and saw the furnace in operation had achance to work the bellows, see the fire, and feel the heat. They gotsome concept of how this was done and learned about one aspect of whathelped us to be where we are today.

"So now they can relate to a piece of history in a way they wouldnever 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 degreein archaeological science. He came to UA's Materials Science andEngineering program because "I decided I wanted a much better, harderscience background as I was proceeding down the archaeology road," hesaid.

Jeffery's research is part of UA's Heritage Conservation ScienceProgram. Students in this program learn to stabilize, preserve andbetter understand ancient artifacts and how they were created and used.

The curriculum, which combines engineering, anthropology,architectural history and art history, is particularly important todaybecause many of the material links to our past are disintegrating,while the ancient technologies that created them are disappearing.


Story Source:

The above story is based on materials provided by University Of Arizona. Note: Materials may be edited for content and length.


Cite This Page:

University Of Arizona. "Making Iron The Old-Fashioned Way Is A Tricky Business." ScienceDaily. ScienceDaily, 14 October 2005. <www.sciencedaily.com/releases/2005/10/051011073801.htm>.
University Of Arizona. (2005, October 14). Making Iron The Old-Fashioned Way Is A Tricky Business. ScienceDaily. Retrieved October 1, 2014 from www.sciencedaily.com/releases/2005/10/051011073801.htm
University Of Arizona. "Making Iron The Old-Fashioned Way Is A Tricky Business." ScienceDaily. www.sciencedaily.com/releases/2005/10/051011073801.htm (accessed October 1, 2014).

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