Iron Production Experiment - May 2002

Date: 25, 26 May, 2002

Location: Vinderheima

Premise: If they made iron -- then so can we using the same techniques

Conclusion: We can't do it this way

The Team:

Staff	Kevin Val Dave Kevin Gus
Recorder	Neil Peterson
Leader	Darrell Markewitz

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.

Starting Facts

Smelter

The experiment began with the creation of a smelter. The smelter was created using local slab rock and was 38 cm from the "back right" to "front left" corners by 43 cm across the other diagonal and approximately 38 cm deep. The corners of the smelter were caulked using a local clay. A hole was left for the bellows pipe in the front face. This opening is approximately 2.5 cm by 5 cm.

Charcoal

Many bags of "Royal Oak" charcoal were purchased. This charcoal was then broken up to a rough standard size of 127 cm³.

Looking down into the smelter	The outside of the smelter	The smelter with bellows set up	Breaking Charcoal

Ore

A total of 6 Kg of ore was needed for this experiment. Unfortunately we did not have that much "single source" ore available. The "ore" for this experiment came from two sources:

• 4.8 Kg of Ore from L'anse aux Meadows (mostly 1cm size) [FeO₃ 6x% + Si + H₂O]
• Forge scale (flake size 2-3mm) ["pure" FeO₂]

Bellows

The bellows were constructed on the day of the experiment. Following the smelting it was determined that each single "pump" of one side of the bellows produced between 2.4 and 2.9 litres of air. The rhythm used in pumping the bellows averaged 63 beats per minute. An average volume of 2.8 L of air per minute is assumed.

Measurements

Care was taken in the measurements used in this page but some margin of error does exist. Especially in the conversions between imperial and metric units. Chemical analysis performed by Marcus Burnham. These analyses can therefore be considered totally accurate.

Roasting the Ore.

This was accomplished using two propane forges. The first employed a can containing approximately 460 cubic cm of ore in a layer 3 cm thick. The second employed a flat pan with a layer 1 cm thick. The can roasted a batch of ore approximately every 15 minutes. The pan was much faster averaging 3 minutes per batch. The roasted ore was weighed at 2.95 Kg. The weight being reduced by 38.5% matches well with the analysed water content of the ore being removed. Two samples of the ore (approx. 0.025 Kg each) were removed for analysis. A lot of discussion occured about the best way to accomplish the roasting. The small size of the ore grains led to a fair bit of dust also being lost. Compare the colour of the unroasted (in can) and roasted (in pan) ore.

Roasting Can of Ore	Roasting pan of Ore	Pan of roasted ore	Roasted and unroasted

Preparing the "charges"

Due to the low silicon level in the ore used it was mixed with sand. The ore was split into three sections.

• 0.9 Kg was mixed with 0.1 Kg of sand. This is refered to later as the "carbon charge" or "third charge"
• 1.8 Kg was mixed with 0.2 Kg of sand. This is refered to later as the "second charge"
• The remaining 0.2 Kg was mixed with 0.7 Kg of sand. An additional 2.4 kg of furnace scale was added. This is refered to later as the "first charge".

Heating the smelter

Absolute Time	Elapsed Time	Notes
1225h	0	A small wood fire was lit in the smelter to begin slowly heating it and drying the clay caulking
1350h	T+1:25	The smelter was filled with charcoal and the bellows were brought into use to begin heating the smelter to operating temperature

Small wood fire	Charcoal fill	Adding air

Smelting the ore

Absolute Time	Elapsed Time	Notes
1441h	T+2:16	The "first charge" was placed on a board in the smelter which was then "topped up" with approximately 4 kg of charcoal
1503h	T+2:38	A problem with the bellows caused the air flow to be stopped
1511h	T+2:46	Bellows air flow resumed
1520h	T+2:55	A sample of the slag was removed by inserting and removing a 0.6 cm iron rod
1544h	T+3:19	The smelter was topped up with charcoal
1558h	T+3:33	Bellows stopped and the second charge was placed in the smelter on a board. The smelter was again topped up with charcoal and pumping was resumed on the bellows
1628h	T+4:03	The smelter was topped up with charcoal
1650h	T+4:35	The smelter was topped up with charcoal
1708h	T+4:53	The smelter was topped up with charcoal
1732h	T+5:17	The smelter was topped up with charcoal
1808h	T+5:53	Bellows stopped and the third charge was placed in the smelter. The smelter was again topped up with charcoal and pumping was resumed on the bellows
1835h	T+6:20	The smelter was topped up with charcoal
1916h	T+7:01	Bellows stopped and the charcoal was scraped away for a short investigation
1921h	T+7:06	Bellows restarted
1926h	T+7:11	The smelter was topped up with charcoal
2013h	T+7:58	Bellows stopped and the smelter was broken open and examined
0900h	T+20:35	Final "excavation" of the smelter

First charge	First charge	Fire pattern	Second charge
Kevin Smith	Val on bellows	Third charge	Third charge
Coals burning	Coals burning	Slag leaking out	Groupings of slag
Slag on the rocks	Cooled slag	Open smelter

Examining the results

Measurement	Note
22 Kg	Total charcoal used
0.77 Kg	Metallic (magnetic) slag removed from above blob
0.45 Kg	Slag removed from above main blob
3.04 Kg	Main slag blob removed
0.97 Kg	Magnetic material fron base ash (very small grain size)
1.02 Kg	Non-magnetic material from base ash - including paper scraps
0.57 Kg	Slag removed from front furnace rock above air hole

Excavating	Blowing off ash	Slag	Slag pieces
Slag	Slag	Slag bowl	Removing bowl
Slag bowl	Magnetic bits

Results
We did not find an iron bloom.

Chemical Analysis
Analysis performed by Marcus Burnham

The compositions of the starting materials for the first Iron Smelting Weekend are shown in Table 1. Separate analyses of the total major elements, ferrous iron, and carbon and sulphur were carried out at the Ontario Geoscience Laboratories of the Ontario Geological Survey using X-ray fluorescence, iron titrimetry, and combustion infra-red analysis.

The sample material was “bog ore” obtained from a site close to the historic site at L’Anse aux Meadows, Newfoundland. The material contained a number of discrete components, including aggregated clumps, tubular fragments, and fine powder. In order to determine how the chemistry varied between the different components, an analysis of the average composition was accompanied by separate analyses were carried out on sub-samples of separated “tubes” and “chunks”.

	Averaage	Tubes	Chunks
SiO2	2.24	1.76	3.23
TiO2	0.02	0.04	0.02
Al2O3	3.35	3.66	2.38
Fe2O3	66.53	60.98	66.07
FeO	2.49	2.56	1.38
MnO	0.62	1.15	1.45
MgO	0.08	0.09	0.05
CaO	0.69	1.05	0.75
Na2O	N.D.	N.D.	N.D.
K2O	0.02	0.03	0.02
P2O5	0.12	0.16	0.09
CO2	13.7	18.7	14
H2O	12.63	12.38	11.94

Table 1: Major element compositions of bog ore collected from close to the L’Anse aux Meadows historic site.

The results of the analyses indicate that the bog ore is composed primarily of iron oxy-hydroxides, most likely limonite and/or and goetite (FeOOH), with minimal ferrous (reduced) iron and very low silica contents.  All components of the ore appear to be relatively carbon-rich (most likely present as calcium and/or iron carbonate cement between grains in the chunks and tubes).

Conclusions & next steps

• The furnace scale was too small a size. It settled to the bottom without having a chance to melt
• Next time we use a single source of ore in a large "chunk" size

We revisited this smelter two years later and took the following pictures showing how it weathered.

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.