Wednesday, November 02, 2011

Stone Age to Iron Age?

The question posed was "could [North American] Pleistocene man have made iron (by accident)?" From a user story perspective seemed easy enough: Man camps at base of mountain (with ore outcroppings); man uses iron ore boulders as fire perimeter; man builds massive fire (i.e.: tribal celebration): Mother nature helps with proper environmental conditions (perhaps storm or strong wind surges);Fire burns to ashes while all sleep. Next day - small lumps of partially reduced ore (iron) found in remains of fire.
Thomas - Missouri

First thing : No one has figured out how people originally figured out that red crumbling rock could be made into anything like metal - or how it was actually done in practice.

(I had to do some Google / Wikipedia work here to supply some dates for the next bit - which because of the sources have to be taken with a grain of salt.)

Humans show in North America something like 15 - 10,000 BC (depending on what research you look to). The first record of human copper working is something like 9000 BC, but that is in the Middle East. I found some references to copper use in the Great Lakes area to something like 4000 BC. First record of actual copper smelting in the new world is not till 600 AD - and that is in Central America.  Balanced against this is that the bulk of tools used in North America remain stone - up to European contact.  I'm not sure North Americans (specifically) ever independently developed any smelting technologies.

Meteoric iron is known in ancient times, but as far as I am aware, the only surviving artifact examples are mainly from cultures that already have some metal working experience. Meaning working native copper or gold, which was found in alluvial deposits in lumps big enough to cold hammer work.
In North America, the exception I know of are the Inuit of Canada's North, who would pick up iron meteors off spring ice, then cold hammer fragments into small points and edges. (In fact there is was a well documented huge meteor that was exploited seasonally - until the Smithsonian grabbed it in the late 1800's!) Note that most of the earliest iron objects from the Old World are also iron meteors - indicated by the high nickel content (sometimes 7 - 15 %.) Metallic iron without nickel is the signature of human produced material.

So a case might be made for applying copper working traditions to extremely rare meteor fragments - working cold.

Generally, the first regular intended production of metallic iron is set at something like 2500 BC, again in the Middle East. (For an overview see the Wikipedia topic "Iron Age" ) There has been suggestions made that there is a relationship between copper ore smelting process, using ores 'contaminated' with iron oxides. (Small ball bearing sized fragments of metallic iron have been found in slag blocks remaining from copper ore processing.)
There certainly appears to be a human progression from ceramic kilns to copper melting furnaces to copper smelting furnaces into iron smelting furnaces (which in turn get larger and hotter - and more efficient).

As to the concept you mention : Rocks with ore + hot fire (hardwood + wind) = reduction to metal

Reducing iron oxide in ore down to usable metallic pieces is considerably more complex than just applying heat.

I certainly have seen a number of times that a too aggressive ore roasting fire has resulted in slag formation on the surface or as small fragments remaining in the later ashes. This likely indicates local patches of reduction, but this is only part of the larger complex series of reactions that converts iron oxide ores into usable metallic iron.
(A good explanation is in : "An attempt to define archaeo-metallurgy"  by Arne Espelund  - published in 'Early Iron Production" edited by Lars Norbach).
You have to not only chemically reduce the oxide, but also provide some system to sinter the individual particles into a larger mass.  Frankly, the whole working system is so "complicated, but not complex" (as Espelund states) that I can not imagine anyone stumbling on to a working process entirely by accident.

This should not prevent you from experimenting with the process yourself!
Good news is that there are some people who have done some ground work and published excellent operating guidelines for building small bloomery furnaces.

Two notable examples:

the Flue Tyle Furnace by Sauder & Williams :

the Econo Norse Furnace  by DARC :

You may be eventually looking more towards earlier / more primitive bowl shaped furnaces. To that end, take a look at some of the (excellent) experimental work being done in Europe, primarily at those at various living history museums.

As regular readers know, I often source blog posts from detailed replies I make to specific questions that come in as personal e-mails. Take this as both a complement, and the 'cost' of getting a detailed reply to a question sent!

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