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Monday, June 16, 2008

DARC Spring Smelt

(duplicate of entry on 'Hammered Out Bits')

This is a very fast report on the DARC Spring Smelt on June 14.

Attendance was lower for this one. The core team was:
Darrell Markewitz / Ken Cook
Notes, Charcoal (and other messy jobs) - Anne Graham
Strikers - Neil Peterson / Richard Schwitzer
Smelter construction - Sam Falzone / Richard

As reported earlier, the intent of this smelt was a full scale test of Gus Gissing's DARC Dirt One - primary bog ore analog. A new standard 'Norse Short Shaft' furnace was constructed. It was decided to make two alterations from the earlier tests:
The analog had shown a tendancy to produce a crumbly high carbon bloom, a type which often proves difficult to forge down to a working bar. For that reason is was decided to increase the average particle size. The dried plates were lightly hammered through a 1 inch wire grid, then screened through a 3/16 inch mesh to remove the fines. This resulted in a slightly larger size than the last two tests.
Second, it was decided to charge very heavily right from the start. Ore was added at one to one against charcoal (2 kg ore with 2 kg charcoal).

We used 20 kg of the bog analog and got a very nice small bloom at 1.8 kg.

Those numbers need a bit of massaging to compare to our past work:

The ore number is actually higher than reality. That's because the analog is mixed with water, and the paste was air dried. There will be some content of water still remaining. I have to take a measured sample and put it into the gas forge on a pan to get a 'dry weight' that would relate it back to the roasted rock ores we have been using. On the last test, the analog was also air dried, and after baking the water content removed was about 12%.

The bloom weight was taken at a different stage in the process than what we normally use to take that measurement. Normally we pull the bloom and work over the surface for one heat to knock off the real 'frobby' bits. This is when the production weight is recorded. For this bloom, which was pretty 'juicy' we had put it back into the smelter with more charcoal (using the smelter like a big forge). We ran through two more hammer cycles, compacting it down to a very rough brick, then one more to slice it in half. So there would have been a bit lower comparative weight to others.

Taken together, this does put our yield down into the 10 - 15 % range - not into the 25 - 35 % range we have come to expect.

We were running this smelt with a bit less air than normal. By the anemometer, we started in the range of 450 litres per minute, eventually working up to closer to 750 LpM. Our consumption of charcoal was averaging about 10 minutes for a standard 2 kg bucket.

We are going to have real good slag volume numbers on this one (to send to Arne Espelund).
First the smelter itself came through the smelt with almost no internal damage at all. There was some erosion just BELOW the tuyere. The slag bath started out sitting a bit higher than normal. We had to poke through the bottom of the bowl as it first formed to drain it a bit lower to keep the tuyere clear. I think that might be the reason. There was no noticeable effect to the smelter wall above the tuyere at the usual hot zone. The inserted ceramic tuyere was hardly effected at all.
We were just getting everything ready into the very end of the burn down phase when the furnace decided to self tap. It was like the waters breaking in a pregnancy. Pretty much all the liquid slag ran out all at once. This was the dark olive green / black real runny stuff. I got concerned that this would expose the top of the bloom to the air blast, so quickly decided on a bottom extraction and reduced the air and got working to yank it all out. There was a very clear volume of slag that formed the bowl itself that was pulled clear. When we grabbed the bloom, there was a third type of slag adhered to the outside of it as well. The analogy of the chocolate covered cherry is perfect here. I will be able to pretty much separate out the three types, and gather all of the slag for weight later.

The bloom feels like nice iron (I've not photographed or spark tested it yet). It is a bit on the crumbly side, more larger blobs hanging together than the nice dense rock blooms you always achieve. Better cohesion than the 'brown sugar' effect you saw at the Smeltfest test of the ore analog. I know its going to be easy to forge this one to bar, the initial consolidation went very smooth, no slitting or fracturing at all.

I'm very pleased with the overall results. The smelter came through in almost perfect condition. We were able to predict and modify the sequence to get around the tenancy of the ore analog to absorb too much carbon and not fully sinter together. Neil and Ken worked as an excellent and smoothly functioning team.

I have to find my actual notes from the day, process the images and get a field report together.



Friday, June 6, 2008

Museums in Denmark

(repeated from Hammered Out Bits )
I had quite differing experiences with the various museums I saw in Denmark:

There were three museums I visited that were basically 'old school' styled presentations: objects in cases, extremely limited labels, objects generally grouped by type. The lighting varied, but generally was reduced general illumination, with use of some spot lighting in the cases. Some idea of light levels can be gathered by the quality of the images. (I have some experience with longer 'hand held' exposures, so the clarity and shift in colour will give some indication of the relative amount of light available.) None of the museums I visited had any staff visible inside the collections themselves (admittedly I was there 'off season', but I also spent several hours at each museum).

The National Museum in Copenhagen had its 'pre-history' gallery closed. For them anything before 1000 AD is lumped together. This new presentation includes virtually ALL the Viking Age materials. It was originally scheduled for opening on May 1, but later delayed to May 17.
The Medieval galleries are very clearly old style. The concentration there was on church related pieces, many larger. The stress appeared to be more to 'treasures' rather than everyday objects. Labels were basic: Object / Location / Date - in English and Danish. Sometimes a line or two of context or more detailed description. No registration numbers (very rarely these were visible on the object itself). If there were a group of like objects (commonly grouped by type) they would share the same three lines and have no further method of identifying them. ('Early Medieval Axes' for a group of a half dozen, obviously mixed construction and combat types) This would make any attempt to get more detailed information from the collection viewing almost impossible. You were not normally allowed to take photographs, and there were no detailed 'guide to the collection' type books available. (Separate topic discussing those.) The gift shop was large with an excellent selection of books ranging from popular overviews to quite detailed archaeological reports.
(Group of Early Medieval Axes)

The Roskilde Museum is actually a complex of related buildings and presentations, each with a different theme. I spent my time at the 'History of Roskilde' collection. The building housing the historic collections was originally a warehouse and factory from the mid 1700's, so there are a large number of small rooms with theme groupings. The objects generally were grouped by find location. Again labels very short (and here only in Danish) with Object / Find / Date. The individual pieces were more usually identified by case number, but again registration numbers were not visible. I'm not as sure here what the policy on photography may have been, as I was introduced to the collection by curator Jens Ulriksen. The gift shop was a small display in the lobby, with limited books available, few in English.
(Group of Blacksmith's tools)

The Ribe Viking Museum focuses quite clearly on two aspects of the history of Ribe, with the main thrust of the collection centred on the Viking Age. About the same floor space is dedicated to Medieval, Renaissance, Early Modern objects (with most stress on the earlier materials). Both the building and the presentation itself are more modern, and it shows in the display layout and methods. This unfortunately includes the use of dramatic spot lighting in rooms with a generally quite reduced light level (to the determent of possible photography). One excellent feature of the presentation was a full scale diorama of a section of the Viking Age market. This put a large number of the artifacts in a working context (and included a huge number of other pieces not represented in the collection.) I think officially there was not supposed to be photography, but I did see any number of general visitors taking photos. The gift shop was again large and had a fairly good selection of books, but here there was more space given to gift items. Popular works were generally available in English, unfortunately most of the research volumes in Danish only.
(Glass Working Display)
(Metalworking in the Viking Market scene)

My visit to the Viking Ship Museum in Roskilde suffered from a major renovation and my own focus on research of ship building tools. The room normally containing the supporting artifacts was closed, with a new exhibit documenting the recent production of the replica 'Sea Stallion' being installed. Labels were available in Danish and English, with usually a short paragraph of detail. One detail I did like was the working tools in the boat yard area (all replicas of course) were hung in public view. Each had Find / Museum / Registration number. The main ship hall has the preserved remains of a number of the ships on display, backed by detailed scale models for comparison. This hall has a large wall of north facing glass, so photography was simplified (and permitted). There was also a room with walk on reconstructions of two of the ships (primarily intended as a children's activity room. Much of the complex is given over to the docks, the boat construction yard - with the large number of replica ships and boats floating and in use. As outdoor areas, the photography is excellent, outside of the restricted viewing angles. (see an earlier post for ship images). The gift shop here had a very good selection of both popular and research titles, many available in several languages. Most of the detailed research volumes were related to ships (unsurprisingly), but many of those only in Danish.
(Working Tools - some of the axes)
(Children's area with full scale dressed replicas)

Generally I found all the museum collections I visited had greatly reduced information available to the viewer. In many cases only the barest description was provided 'bunch of axes' being typical. Sometimes the objects were not even given enough description to provide real understanding, for example 'spindle whirls' does not inform you about just what those pieces are. With no registration numbers, it would prove very difficult for the research minded to gather detailed information. Rarely were objects placed in any kind of working context. The collections were almost all presented in a formal and static style (Victorian Cabinet of Curiosities). The Viking Ship Museum was the primary exception, but it blurs the line between artifact collection and an experimental archaeology presentation (which in fact are in two distinctive areas of the complex).

I also spent two afternoons at the Ribe Viking Centre, a living history styled presentation. As this museum was not officially open at the time, and also represents an entirely different type of display style, I will leave a discussion of it for another entry.

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Thursday, June 5, 2008

Iron Smelting 2008

Just a general notice:

I realized yesterday that I was way behind on indexing the raw notes from the 2008 smelting series. At this point there have actually been a total of 7 smelts undertaken. In truth a lot of the materials had been published over on the Wareham Iron Smelting site earlier - but I had not linked any of it to the 'outside'.

Oh - you may also find my last post to Hammered Out Bits interesting - it grew out of a conversation between Neil and myself and another correspondent about museums and presentations...



      Updated: 4 Dec, 2007
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