Thursday, June 19, 2014

Pictish Late Iron Age Smelt - Overview

This will be a fast overview, mainly as a photo essay, on the bloomery iron smelt carried out at Wareham on June 14, 2014.

The prototype is Culduthel, Scotland, circa 200 - 400 AD.
The furnace is a 'slag room' type, with a clay shaft built on a withy frame, over a stone base. The general details of the layout were similar to other Late Iron Age / Viking Age furnaces built in the past. The material used was a 50 / 50 mix of dry clay and course sand.
(See the earlier post : Scottish Dark Ages Iron Smelt )

This smelt was a test / training for the 'Turf to Tools' project being undertaken at the Scottish Sculpture Workshop over August 9 - 25, 2014.

Clay shaft being built up on a wicker frame, over a stone base chamber.
After drying fire - extensive cracking of the shaft (extraction point to right)
Equipment set up, at pre-heat phase.

Adding the DD-SSW1 analog
Bloom mass at initial extraction. Bottom pull was intended, but top extraction was required.
After two initial compaction heats, an attempt to cut the bloom.
Final Bloom : 5.2 kg (from 28.3 kg dry ore = 18% yield)
 The next day, the bloom was re-heated and compacted using the hydraulic press. After cutting to quarters, the interior surface was spark tested. The observation suggests roughly .6 -.7 carbon content, a good blade making material. (!)

The following will be of more interest to the archaeologicallly inclined:

The overall remains from the smelt around the furnace.
Broken pieces of the furnace, clearly showing the imprint of the wicker interior frame.
Furnace opened along the major cracks, showing the slag bowl in place below the tuyere entrance.
Main slag bowl removed as two pieces. The tuyere was to the left.
Cleaned surface of the rock base. Tuyere was to the top.

There will be a fuller report to come on making a comparison between the results here, and the remains seen in the archaeology from Culduthel.

Some General Conclusions:
  • Some modifications to the layout and construction of the furnace may be necessary to :
  1. avoid cracking
  2. conform more closely to the slag pattern at Culduthel
  • The analog used proved quite successful, even if the yield was a bit low.
  • The general progress of the smelt followed the expected pattern.
  • A better system needs to be established for re-heating the bloom for consollodation.
With thanks to the working team:
Kelly, Ron, Heather, Rodger, Neil, Richard.

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

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