Iron ore

[Ironhand]

For my group I am working on a smelting furnace and a smithy. While, I will utilize some local mines I'm curious as to what places one would go to if importing high quality ore. Not interested in cheap, low quality Chinese ore.

Something I am also interested in is the idea of Spanish ore being buried to seperate out the best ore. Is this a practical idea and was it buried before or after being smelted?

[Dan Howard]

Diodorus wrote that the Celts " bury plates of iron in the ground and leave them there until in the course of time the rust has eaten out what is weak in the iron and what is left is only the most unyielding... [V.33.4] There are other references to iron being submersed in salt water to achieve the same effect. I have asked a few metallurgists about this and they seem to think it is bollocks. Burying wrought iron in the ground would destroy the iron first, leaving the slag impurities. It is possible that Diodorus misinterpreted the practice and it was actually some sort of sacrificial ritual, or the iron was buried as a means of hiding it from enemies. It doesn’t seem likely that the Celts buried iron as a religious offering since archaeological evidence has only uncovered finished items such as swords and spears. It could, however, explain the references to salt water since it was common practice to place offerings in rivers and lakes.

However the Celts could produce blister steel. The carbon content in this is very uneven and one method of redistributing the carbon more evenly was "pattern welding". What would happen if this blister steel was buried? Would the softer iron corrode at a faster rate than the sections with a higher carbon content? If this is the case then this may have been what Diodorus was talking about.

[Gobae]

Ironhand - you shouldn't have to get any ore from China. I see you got a location of Alexandria and a Virginia state flag. If you are indeed from Alexandria VA, VA has fine hematite ore and you can probably get some for free (other than the gas to drive). Most companies can't be bothered with small veins and there's probably plenty just sitting exposed near rock cuts or old mines. (Don't go IN the old mines!)

You could get in contact with Lee & Elizabeth Sauder [url:3okhdloh]http://www.leesauder.com/[/url] from Lexington VA. They have EXTENSIVE smelting experience, albeit with neo-smelting. But I'm certain they can help. There's also a yahoo group called "EarlyIron" that discusses all manner of historical smelting.

BTW have you decided on a smelter type? The quickest and easiest to make are the "short stack" or "coupola" type. It was also the most common throughout Europe during the time periods in question. I've worked with a couple and if you're just interested in getting something going before switching to period equipment you may want to take a look at this: [url:3okhdloh]http://www.celticclans.org/projects/smelter.html[/url]

Otherwise the left-most column on this page [url:3okhdloh]http://www.cdblacksmiths.org/scrapbooks/symposium2004.html[/url] is probably what you're after.

Finally, there are 3 main types of iron ore and each has varying levels of iron content.

Limonite (Bog Iron) because of how it's made (by anaerobic bacteria) its real composition is often FeOH+H20. This is the least desirable ore type, but it does work; just ask the Norse.

Hematite is Fe2O3. So the theoretical max yield once the Oxygens are cracked off is 2/3 of charge weight. In reality it's more like 1/3.

Magnetite is Fe3O4. It's theoretical max yield is 3/4 of charge weight, but 1/2 weight yield is more common. Additionally, magnetite is real easy to find; there's so much iron in it a magnet sticks.

There's so much more to talk about, but hopefully this will help.

[Gobae]

Dan - I agree with the metallurgists, that burying wrought iron will just rust away the iron and leave the slag inclusions behind. In fact archaeologists often find black slag stains where items have been held together with iron fasteners. However, this is even worse for steel. The carbon content actually INCREASES oxidation rates.

From the evidence in "The Celtic Sword" by Radomir Pliener it appears that the Celts were widely varied in their knowledge of metallurgy; as one might expect of a tribal group. However, true "blister steel" doesn't seem show up in the archaeological record as a known Celtic technique (AFAIK). Blister steel is a (Late?) Middle Ages technique that expanded on an earlier technique known as "Case Hardening"; which the Celts DID know.

Basically, iron is placed in a carbon rich, oxygen poor environment at 1300-1500(F) for hours at a time. In this environment the Fe will bind with the C since there is no O to get in the way. Since this happens by contact the outer sections of the iron convert first (roughly 1mm depth/hour) creating a steel outer "case" around the iron item.

Blister steel OTOH takes this process to the extreme, with such long "soak" times that nearly the entire iron bar will have been converted to steel. It also leaves distinctive blisters on the bar (thus the name). It also leaves a distinctive pattern behind (similar to that of pattern welding) when it's worked.

Now, that's not the only way to get steel from iron. Remember steel is a NORMAL by product of every smelting operation. It simply needs to be separated out from the bloom as it's being compressed. Or as Dan said, the pattern welding will redistribute the high carbon areas throughout and homogenize the bloom into relatively low carbon wrought iron.