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Iron production weekend - October 2004

Date: Oct, 2004

Location: Vinderheima

Premise: How fast can we build a smelter and produce iron.

Conclusion: Really quickly it seems.

The Team:

Staff Grimbold
Recorder Neil Peterson
Leader Darrell Markewitz
Smelt_cd Reports of all of our iron smelting efforts along with more articles and information are available on the "Iron Smelting in the Viking Age" CD from the Wareham Forge.  Copies of the CD can be purchased here.
For three years we have been refining our attempt to smelt iron using a Norse style furnace (2002, 2003, 2004). Our eventual goal is to produce blooms on the majority of smelts using techniques and materials appropriate to the Norse culture. Three times we've made the effort and three times something hasn't been quite right and our bloom never formed.

From time to time we have given talks about our efforts. The most recent one of these was given by Darrell Markowitz to the Pre-Industrial Iron Symposium at the Farmer's Museum in Cooperstown, NY. The general enthusiasm between the Symposium presenters was contagious. Skip, Lee and Mike convienced Darrell to attempt a smelt using the Viking Age prototype. They succeeded - at least partially.

We got together at Vinderheima to work on various small projects on a chilly October weekend. At least that was the original plan. In discussing the Cooperstown conference it became apparent that we all wanted to see a bloom come out of our smelter!

Grimr and Kjarval quickly sketched out a plan for a "fast" version of our basic design. And "fast" was the definite keyword for this attempt. On our previous attempts we spent one weekend making a smelter, and then a long day running the smelt. This time we broke ground around 1430 and ten hours later we had a bloom!

Once again we would like to express our thanks to Royal Oak Charcoal who donated the charcoal used in this year's experiment. We have used Royal Oak Charcoal in all our experiments as they are a hardwood lump charcoal (pretty much what the Norse would have produced) and their quality is consistently high. From all of us -- Thank You!

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Initial rough layout Side view Top view Morning after sketch

The smelter itself was constructed differently this time. With speed of construction (within our design parameters) being very important.
Absolute Time Elapsed Time Notes
1506h   A hole 55cm across and 25 to 37 cm deep (depending on which part of the not-even-remotely-level ground we measured against). A base of dried clay was laid approximately 4 cm thick (when compacted).
1532h T+0:26 On this base we built a circle of 9 firebricks standing on end (this produced a rough circle 22.5 cm deep and 27cm across). The hole was then backfilled with soil and tamped into place.
1540h T+0:34 The airpipe was rested on this brick and ground outside producing the 20 degree down angle we were looking for. A second circle on fire bricks went on.
1650h T+1:44 At this point is was necessary to mix up some clay to use to caulk the seams between the bricks. During this time we also measured the ore charges from some extra roasted ore we had lying around. 8 chares each of 1 Kg were prepared. The caulking was applied and the outside of the bricks was also given a band of clay.
1751h T+2:45 A third layer of bricks went up and was also caulked with clay. This gave us a total stack height of 67.5 cm, a diameter of 27cm, and a bowl of 22.5 cm depth below the tuyure to hold the slag.
1811h T+3:05 We then raised some large stone slabs into a box around the smelter and backfilled with sand. Then it was time to start a warming fire that would also dry the clay.
1823h T+3:17 To stabilize the airflow, and help with our low numbers of people, this year we were using an old vacuum cleaner with a rheostat to control the power and hence the airflow. The air was turned on to level "A" (just enough to start an air flow).
1910h T+4:04 Airflow was increased to "B".
1945h T+4:39 Airflow was shut off for a moment while the smelter was filled with charcoal. Airflow was then restored. This is a good point to mention a minor change in our handling of the charcoal. This year with our "fast" concept (and rapidly approaching night) we did not screen the charcoal but did a visual inspection to keep the chunk size down. Larger pieces were broken up with an axe.
1957h T+4:51 the charcoal level had dropped by 15 cm (more on the tuyure side, less on the back). The smelter was re-filled with charcoal.
2001h T+ 4:55 The airflow was increased half way up to "C". This produced a nice loud "jet-like roar" from the smelter.
2008h T+5:02 Temperature check with the optical pyrometer. 2950 deg. F. Too hot. So we reset the air to "B". More charcoal was added as the level had dropped 10 cm.
2020h T+5:14 It just wouldn't be us if SOMETHING didn't go wrong. This time the power cut out and we lost airflow. For the next 19 minutes we had intermittent airflow. The good news is that at this point we were only warming the smelter so it didn't really impact us. Also during this time the lovely blue flames of a reducing fire appeared above the charcoal.
2033h T+5:27 10 cm of charcoal added (power still intermittent)
2044h T+5:38 10 cm of charcoal added.
2059h T+5:53 Temperature now 2580 (F) and the first charge or ore was added. 7.5 cm of charcoal was also added.
2114h T+6:08 Ore charge #2 was added along with 10cm of charcoal.
2125h T+6:19 Ore charge #3 was added to the back half of the smelter and 7.5 cm of charcoal.
2134h T+6:28 Ore charge #4 was added to the back half of the smelter along with 12 cm of charcoal.
2144h T+6:38 Ore charge #5 added to the back half with 10cm of charcoal. At this point charge #1 should have worked its was down to the "hot spot" in front of the tuyure. Another temperature check was made showing 2520 (F).
2151h T+6:45 The burn seemed a little high to us so the air was reduced to A+ 3/4. The "jet roar" had been getting louder for the past little while. Reducing the airflow left the roar going but without as much volume.
2152h T+6:46 Ore charge #6 was added to the back half with 10 cm of charcoal. By now the first two charges should have been in the hot spot.
2207h T+7:01 Ore charge #7 added to the back half with 10 cm of charcoal. At this point the first 3 charges should be in front of the hot pot.
2222h T+7:16 10 cm of charcoal added. The first four charges should now be in the hot spot.
2237h T+7:31 10 cm of charcoal added. By now five charges should be in the hot spot.
2250h T+7:44 10 cm of charcoal added. At this point 6 charges should be in the hot spot with the final charge only 5 cm higher. Around this point we observed that additional yellow (oxidizing) flame was appearing across the surface of the charcoal. Lots of blue flame still.
2303h T+7:57 The reduction charge was added across the clear burn line (about 1/3 of the way back from the tuyure) along with 7.5 cm of charcoal.
2319h T+8:13 10 cm of charcoal added. Yellow flames had mostly vanished by this point.
2331h T+8:25 7.5 cm of charcoal added.
2343h T+8:37 10 cm of charcoal added. Some yellow flames are beginning to reappear. The reducing charge should be about 10cm above the hot spot.
0002h T+8:56 The charcoal level had dropped 15 cm so we decided it was time to empty the smelter. Note that it was now 2 minutes after midnight -- a true DARK event! Airflow was reduced to "A"
0004h T+8:58 The first charcoal was scooped out the smelter.
0015h T+9:09  
0021h T+9:15 First two bricks are now visible and the bloom was very apparent.
0023h T+9:17 We used a large (wet) log to pound on the bloom while it was still hot to consolidate it as much as possible before removing it.
0035h T+9:29 Two lumps of slag came out on the scoop.
0036h T+9:30 The bloom was pulled out, set on a rock and pounded on by Darrell. This was interesting to watch as you could see the lump jump from the force involved but very little compression was achieved.
0039h T+9:33 Final photos of the bloom and head inside to celebrate!

The next morning we went out in the rain, took a couple of final photographs and brought the bloom in. A quick test with an angle grinder produced an impressive shower of sparks (medium carbon coloured) and a very bright shiny metallic surface.

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Flat base Backfill Second row Clay packing
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Third row with packing Backfill Preheat Charcoal burn
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Bloom Empty Smelter Bloom with ground spot Bloom
Bloom bits


Time to burn charcoal
Unlike our last carefully measured kilos of charcoal this time we recorded the depth of charcoal added. Volume of charcoal burned over time is simple math at that point (Pi * radius squared * depth).

Time (min) 12 11 25 11 15 15 11 9 10 8 15 15 15 13 13 16 12 12 19
Depth (cm) 15 10 10 10 7.5 10 7.5 12 10 10 10 10 10 10 7.5 10 7.5 10 15
Volume (cubic cm) 8585 5723 5723 5723 4292 5723 4292 6868 5723 5723 5723 5723 5723 5723 4292 5723 4292 5723 8585
Rate (cubic cm per min) 715 520 229 520 286 382 390 763 572 715 382 382 382 440 330 358 358 477 452

Please note that these charcoal depths were approximate. On our next smelter we will add some clear marks to make these measurements more accurate.

When we looked at the smelter the next morning there was minor damage on the two bricks above the tuyure. We could have reloaded the smelter and run another smelt.

This time we had clearly addressed the air flow and slag bowl issues we had faced in our previous smelt.

Concepts for next time

Smelt_cd Reports of all of our iron smelting efforts along with more articles and information are available on the "Iron Smelting in the Viking Age" CD from the Wareham Forge.  Copies of the CD can be purchased here.
      Updated: 4 Dec, 2007
Text © Neil Peterson, Darrell Markewitz, 2007
Photographs © Individual artists
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