Friday, June 13, 2008

Ores and Furnaces in 'the Colonies'

Jens wrote:

The Heltborg ore is correctly from "Guldforhoved" nearby Herning, and one of the sources that have been used for a lot of experiments in Denmark during the years.

Thanks for that.
I really noticed two big differences between the general approaches used in Denmark and what we have been doing here in North America.

We don't 'really' have any history of really small iron bloomeries in NA. There might have been something like the Evenstad furnaces used in the very earliest days of colonization - basically in the 1700's. But the general trend then was to build larger blast furnaces instead, the normal technology of that period. There is also a strange attitude in the days of the early colonization. In the first days of any settlement there was often some small scale testing, maybe some limited production. The concept
was to first prove the value of the colonization efforts, then attempt to 'make them pay'. This never worked out, and pretty fast certain agricultural production (tobacco for one) was shown to give much better return for effort. Once the new settlements were developed, often industrial development was actually discouraged - to keep the colonies dependent on the host nations for finished goods. So it was often much later (closer to the 1800's) before any serious North American industrial iron production took place.

So what we have here as inspiration are bits a pieces of not very clear archaeology to read about from a remote distance. As you know, even finding any kind of descriptions is not easy, and many are not clear (or as we have so often found, just plain wrong). In Denmark you have all these slag blocks and some furnace bases to actually go out to look at.
For that reason, the stress here in NA has been on actually making the iron, not so much on matching the layout of the furnaces or duplicating the slag remains. Frankly, I have always treated the slag as a waste product that is just in the way. The furnace is just a tool to make iron, and considered a largely disposable tool at that. For my first number of smelts, I had been making a brand new furnace every smelt.

The second big difference has been the quality of the ores we have been using. The stuff from Virginia is all from an ancient sediment that lays under the Blue Ridge Mountains. It is like a fossil bog ore, hardened to stone - and very pure. Skip and Lee have been generous giving away their stuff, which we pull right out of the rock layer. The stuff that the Williamsburg team is using is the same material that has eroded out and washed away to a new surface deposit. In either case, the iron oxide content of this stuff is in the range of 80 - 85 %. *
The primary bog ore I pulled from Newfoundland tests out to be even purer - close to 90% iron oxide.
And the other materials I have been using (commercial taconite, hematite grit) are also in the range of 95 % iron oxide.
You can see that making blooms from ores that pure might get you working in a certain way.

If anything, I certainly have worked with a LOT of different ore types!
- L'Anse aux Meadows - primary bog ore
- St Lunaire - primary bog ore
- Taconite (Stelco) - commercial
- Virginia (Lexington) - geothite
- Hematite (grit) - commercial
- 'DARC Dirt 1 - 'Spanish Red' analog
and at Heltborg
- Guldager - 'ancient bog ore'
- Guldforhved / Guldager / Tranemo - blended

I never did get any numbers from anyone about the various ores from Denmark. Here would be either the Guldforhoved or the Guldager ores used at the symposium. (I'm hoping others can supply any hard numbers on iron oxide content for those?) I heard a lot of comments about 'good ore', but never any numbers that could be used for comparison. In comparison, the team from Tranemo did mention their ore being something like 70 - 75 % iron oxide. This compares with some of the materials we have been using here. At Helborg, the Swedish team were able to consistently pull out good working blooms every smelt they undertook.

Although there was a lot of talk at Heltborg about how I was running my furnaces differently than most of the rest of you, at the most basic level, I don't think that really was that important. I feel it was the ORE that creates the problems. I may try a couple of smelts here using our ores here with the slightly slower burn rates that Michael Nissen was using. I'm less convinced, because I did undertake a number of smelts at the beginning with lower air volumes (so slower burn rates) and never got any iron produced. As soon as I learned about the higher air volumes from Skip Williams and Lee Sauder, using their basic method instantly gave me positive results. Large solid workable iron blooms!

* Figures corrected after I had this comment come in from Lee Sauder:
I looked at your blog this morning- you've misspoken- our brown ores have generally indicated 80- 85% iron oxide (as Fe2O3).

Lee also referred me back to the analysis done by Marcus of DARK, one of the very few chemical tests we have ever been able to have made.

(Thanks - Its pretty sad when you can't even remember your OWN past work!)

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February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

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