Wednesday, October 19, 2016

Turf to Tools 2 - Smelt 3

Continuing the descriptions of the work under my OAC Project Grant...

The third smelt undertaken as part of Turf to Tools 2 was an extra one.
Eden Jolly and Uist Corrigan (SSW staff) did most all the work on this. My contribution was some helpfull advice, breaking ore, and as striker at the end.
Eden (sitting) and Uist - at the start of the sequence
Slag running as part of 'constant tap' process
This smelt was primarily intended to let Eden and Uist see that they had acquired the basic skills for the bloomery furnace process. To that end, the proven furnace layout from smelts 1 & 2 was used. Ore chosen was primarily industrial taconite pellets. A number of recent modifications (well illustrated at the Poland Symposium) were also incorporated:
- Initial charges of 3 kg iron rich slag (Nissen)
- Continuous slag tapping (Sauder)
- Addition of partially sintered gromps (Sauder & Williams)
Resulting 9 kg bloom, partially compacted and cut
Furnace : Short Shaft on stone & block plinth
Build : standard clay / sand / manure mix (repair from smelt B)
Size : Tapered 25 to 20 cm ID, 68 cm total with 50 cm stack and 30 cm to hard base
Tuyere : tapered copper, 5 cm proud, 20 degree down angle
Ore : Industrial Taconite (22 kg) + Lecht Mine (6 kg) + smelt 2 gromps (6 kg) - total 34 kg
Fuel : hardwood charcoal broken to standard size
Method : 3 kg iron rich slag added as first charges

BLOOM : 9 kg, fragmented - yield 26 %
Larger piece, after cutting and breaking
The next day, the lads cut the larger bloom piece with a zip disk, also breaking through the central portion at the bottom of the cuts.
Enlarging the image above may prove interesting. Note the large size of the broken crystals, and the very white colour of the metal there. Both are visual indicators of a higher than normal carbon content to this bloom. Spark testing confirmed that the iron produced was 'steely' - consistent with a roughly 0.50 % carbon content (similar to a modern spring steel). When fully compacted, this should prove a good tool making material!
Furnace just after extraction
Another important result here was the construction of the furnace itself. The basic layout was still based on the Pictish archaeology at Cudulthel. Another element used by Lee Sauder was incorporated, that of a large extraction arch built into the front base of the furnace. This is sealed separately with a new wall of clay cobb before each use, making this area easy to remove without placing strain on the remainder of the furnace itself. As you can see in the image above, after 3 complete smelts, the main body of the furnace remains in good enough condition (with some cracks repaired) to continue in use.

Excellent work!

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

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