Back in 2005, I took part in an event at Tekniska museet (the National museum of science and technology) in Stockholm where we demonstrated pre–industrial Swedish and Japanese techniques for iron and sword making. Quoting another post that I wrote two weeks ago:
Those of you who read Swedish may have seen that there is a page on my blog called “Svärdens mästare”, which translates to “Master of the swords” in English. I transferred this page without further ado from my previous web site and have yet not taken the time to translate and rework it. The page is a brief account of an event at the National museum of science and technology in Stockholm in 2005 where Swedish and Japanese metallurgists, swordsmiths and others participated. Myself I was responsible for the construction and operation of a shaft furnace representative of pre–industrial iron making.
I finally decided to remove that old page. I’ve therefore decided to write this fairly lengthy post for future record. Below, you’ll find some information about, and photos from, the event, which took place at the National museum of science and technology in Stockholm on September 10 and 11, 2005.
As mentioned above, a lot of parallel activities took place during the weekend at the museum. However, from my perspective, the most important activity was the construction and operation of a coal–fired shaft–type bloomery furnace. I had been involved in the planning of the event since several months, and I and the furnace group members, who were students at Högskolan Dalarna by that time, had learned and practised furnace construction and operation in advance.
During the summer we had been on a two day camp at Hammarede smithy to learn from the experienced K.-G. Lindblad who had been making bloomery furnaces for 20 years. We had then constructed and operated a furnace in Borlänge only a few days prior to the event at the museum.
Under K.-G.‘s supervision, we managed to complete two runs at Hammarede. K.-G. also helped us to forge the loupes, or blooms, into small ingots of about 1.4kg each. The loupe is first compressed on a stump in order to make use of the heat from the furnace as seen in the big picture at the top of this post. After that comes a lot of hard work in the smithy before you have those beautiful compact ingots seen above.
After the summer we built a new furnace in Borlänge which was to be demonstrated during the introduction of new students at the Material design programme.
Our furnace was a copy of the one we used at Hammarede. Variants of this furnace type has been used since the iron age, and was, despite the invention of the blast furnace, still used for small scale iron making until the 19’th century in some areas. A patent for an improved furnace, similar in principle but fired with stone coal instead of charcoal is described by Herbert (1849). Apparently this furnace was still considered industrially important in the early 19th century.
We were encouraged when, despite some difficulties, we managed to produce a nice iron loupe.
The height of the vertical shaft was determined from our design with two layers of vertically standing bricks put on top of each other. The shaft was supported by an insulating layer of gravel contained inside a log wreath. The arrangement of bricks can be seen in the drawing and photo below. The photo shows the condition of the furnace after the run on September 2. We had quite a bit of a problem to get the loupe out of the shaft, which resulted in severe damage to the furnace.
Peter Matsson made the wreath for the Borlänge furnace seen above. The fancy log wreath seen in the pictures below from the museum was made by a professional carpenter.
The furnace at the museum
On Monday, September 5, I drove from Borlänge to Stockholm together with Robert Ståhl to construct the furnace at the museum. We brought a trailer fully loaded with timber, bricks, clay powder, as well as the tools needed for construction and operation. I had also arranged for one m3 of rough gravel, as well as a pallet of charcoal, to be delivered in advance at the museum.
During Monday we constructed the furnace that would be used during the next weekend. The shaft was laid with clay and vertically standing bricks. It was lined with clay on the inside and a log wreath was used to contain the insulation, consisting of approximately 300kg gravel and soil that we dragged across the museum’s yard in 10 litre buckets.
Bricklaying is a messy story. The mortar consists of clay, sand and horse manure (if available), mixed with water to a fairly loose batter. The best finish is obtained if you work with your hands as the mortar is placed on, and smears with water so that the surface becomes smooth and fine. When then furnace is ready, it is dried through slow heating by wood without blasting, until the moist has been driven out of the mud. At this stage, heating should be quite cautious in order to avoid cracking.
Then, on Friday September 9, we went again with a fully loaded trailer from Dalarna in the direction of Stockholm. More than a few people were probably turning their heads when we passed, because the trailer was dominated by a large bellow — our newly built two chamber bellow with an estimated bladder capacity of up to 800 litres per minute. In addition, we brought fire wood, iron rods, pliers, some stumps and other stuff needed for the furnace operation.
We made one run each on Saturday and Sunday. Each time we charged a total of about 10kg ore added in amounts of about 1kg every 20 minute. For each charge, we added about twice the amount of charcoal. Discharging of the loupe was scheduled for two o’clock, and by that time a fairly large crowd had gathered to see the show. This time we managed to get the loupe out of the furnace without too much trouble. Worse was that the process took longer than expected, but the crowd seemed to be patient and people stayed around until the end.
About 1500 people paid the entrance fee to visit the museum during the weekend. An unknown number of people chose not to pay the entrance fee, happy to stroll around and look at the activities outdoors.
My rough hand drawn schedule for the duration of the three days, which I made before the event, is seen below. This reflects my estimates in advance. However, the actual outcome correlated fairly well with the plan.
A number of interesting activities took place in addition the our furnace. A professional Japanese samurai sword polisher worked for two days in the museum. There were demonstrations of the Japanese traditional ironmaking in a tatara furnace. A Japanese blacksmith made tools and axes in a small forge — he stood in a hole that he had dug in the sand outside the museum. Rolled bamboo mats were chopped up using samurai swords (katanas) and beautiful 1200AD style European swords forged by Peter Johnsson. I’m not going to write about that now, not because of a lack of interest, but because with this post I wanted to document our ironmaking efforts.
We received some good publicity the days prior to the event. On Friday September 9 there was half a page in SvD on showing Japanese and European swords, supplemented by photos of our installations at the museum. DN “På stan” containd a note about the event. TV4 were broadcasting live from the museum during the culture news. Our bloomery furnace was seen in the background while we fired to dry the furnace. Channel 1 had made a recording from the museum during the day before and showed it during their culture news on Friday. Since nobody else wanted to be on the radio, I myself had the pleasure to have a five minute conversation about swords, samurai’s, and ironmaking live in Radio Stockholm.
In addition to the information here on Manufacturology, two reports from the event are available if you read Swedish. Immediately following the event I wrote an article which was published in Bergsmannen [Storck, J. et al., “Svärdens mästare möttes”, Bergsmannen, nr. 6, 2005] (in Swedish). You can download it here: Svärdens mästare möttes (757 kB). The ironmaking technologies, i.e. the bloomery furnace and the tatara furnace, were also described in another article in Populär Arkeologi: [Magnusson, G., “Samurajer och vikingar — så smidde de svärden”, Populär Arkeologi, nr. 3, 2005] (in Swedish).