Friday, November 02, 2012

Iron Smelt in Russia?

 (This is a much older piece that got caught as a draft somehow and I think never posted...)

This video clip was suggested by one of the Early Iron gang:

The clip shows a team from Russia (given the Cyrillic text) working at a large living history (Viking Age?) event.

I quite like the simplicity of the basic construction method. Use of bundled straw for interior form is elegant.

I do wonder at the purpose of the base construction.
The built up earth plinth may be primarily to raise the height of the furnace. This appears to be explained in commentary. Other than raising the furnace for ease of access, its hard to understand why.
Considerable care is taken with the construction of the base, with a layer of straw, covered with a clay cobb plate, this in turn with what appears to be a semi refractory layer. (Light coloured clay that appears to be mixed with charcoal fines.
This same light material is used as the inner layer for what looks like the first 10 cm of the furnace wall.

The interior diameter of the furnace looks to be roughly 20 - 25 cm.

Note the bellows size and style (medium size double action - Late Medieval) Depending on pump rate (hard to determine from the video) this equipment should be able to supply plenty of air volume.
Use of steel pipe for bellows tube / tuyere
Set at basically flat angle (only slight downwards)
Very shallow base distance below tuyere (perhaps 10 cm??)

The is use of round port for tapping. Appears to be at same height as the tuyere.
There was no tapping event recorded, and no tap slag visible in later parts of the smelt.

Total furnace height looks quite short, the entire furnace may achieve (barely) 40 cm total. Considering placement of the tuyere, this suggests a very short reactive column.

Charcoal is roughly broken for size, scoop from pile method for screening out fines.

Ore appears to be hematite / iron sand or oxide powder (brown ochre) ?
Laid in a large slabs rather than sprinkled through charges. Only two charges shown, and it would be important to know how much ore was used.

There is use of flux (a fine white powder - may be borax?) near end of smelt.
May be explained in commentary, but why?

Furnace is allowed to burn out and basically go cold.
Extraction is by breaking out rear wall to expose interior.

When the interior is exposed, the slag mass certainly looks considerably above the height of the tuyere. Was the smelt halted because the tuyere was blocked? (Commentary may explain?)

On the extraction, three pieces are pulled aside.
The first (which is the piece in the smelter's hand near the end) is holding heat in a manner that at least suggests there may be some iron in it. If so, it is extremely lacy and small. The second piece is dense and dark, and looks like iron rich slag. The last piece (seen again near the end of the video) is light coloured green, typical of an iron poor slag (melted furnace walls).
Obviously the comments of the team would be important to understanding their results.

It appears the smelt master has determined the pieces containing iron by look and weight. It might have been more instructive (for him and us) if these fragments had remained hot enough that they could have been hammer compressed


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

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