I was sent this and felt some members here may find it interesting. Just watch your volume.
Bog Iron burning in Budalen - Norway
- Thread starter Teegate
- Start date
You have to watch the entire thing. Very tedious process. There is no dribble out into the pigs from a molten bath. Yes, very small scale.
This seems to match more or less with R.B. Gordon's description of bloomery work (American Iron, pp. 94-97), but on a very small scale: look at the tiny bloom they lift out at the end! He gives a good description of the work, and of the ineffable skill required both in manipulating the materials in the fire as the bloom formed and in hammering the hot bloom under a triphammer. His description is based on the Adirondack bloomeries of the latter half of the nineteenth century, where the art of blooming had reached its global zenith and ran very near theoretical efficiency, achieving something like a 5-fold improvement in fuel-to-iron ratio over the Revolutionary-era northern New Jersey bloomeries. (They started experimenting with magnetic separation basically as soon as Joseph Henry developed practical electromagnets in the 1830s!) He does cite the Evanstad treatise mentioned in the video (from 1782).
I had overlooked the importance of ore roasting. Gordon suggests that ore of at least 55% iron content would be necessary to form metal in the bloomery. That seems like a remarkably high figure (so maybe it's specific to the highly refined Adirondack technique); Rogers' analysis gives 45-48% iron content for (hydrated) Atsion bog ore, so roasting would seem necessary to raise the iron content and probably also to make the ore more uniform in texture. Given the difficulty of the forgeman's task, I presume they would want their ore to be as consistent as possible. Roasting could be done pretty simply on the ground, of course, but given the scale of the task, it was probably more convenient to construct some kind of roasting vessel: http://iron.wlu.edu/reports/RoastingOre.htm Of course, if the roasting oven was basically a big iron cauldron, it could easily be hauled away and scrapped at the end of the iron era, leaving little trace on the landscape.
Fascinating, so roasting the ore would have been advantageous, yet I don't recall mention of a roasting step addressed in the various papers on ore raising here in the New Jersey Pine Barrens. Is there a reference to roasting ore in South Jersey?
There seems to be very little, but then again, a lot of the little scraps of practice in things like Drinker's letter or the Martha diary would be incomprehensible to us without a more full picture of iron operations elsewhere. There's an account of practice at Nassawango Furnace on the Delmarva, which operated in the 1830s (https://books.google.com/books?id=6GdDAQAAIAAJ&pg=PA314) and used ore-raising methods that sounds similar to those employed in the Pines. If I interpret it correctly, they roasted the "hard" or massive ore to break it up, but perhaps not the softer loam ore. Accounts of practice at the end of the period (e.g., Overman's treatise) suggest that bog ore should always be roasted, but who knows whether this was always carried out.
The Martha diary for March 24, 1811 has the entry: "All gone well. Ore heap afire. Ore teams carting sand." The second sentence suggests a roasting operation to me; the diarist doesn't make it sound like a catastrophe (the sand is for molding).
My impression is that Gordon's caveat about needing ore of a minimum 55% iron content for successful bloomery smelting probably applies to bloomeries in general, which seem to have consumed higher-grade ore and of necessity produced fairly iron-rich slags. Given the general fussiness of the blooming process, I suspect roasting would have been necessary in general for bog ore fed into a bloomery forge in order to produce anything like consistent, quality iron, but this is speculation on my part. The simplest form of roasting would have been simpler than charcoal burning: just make a gridiron of logs, heap ore on it, ignite and allow to burn (no turf necessary)!
I know in the Piedmont and Ridge & Valley, old charcoal flats can be detected on LIDAR from their alteration of contour and field-checked by the detection of a charcoal layer in the soil; has this been done in the Pines as well? Presumably a roasting site would look similar but leave a mixture of charcoal and powdered ore somewhere in the soil.
Note that the high iron content of bloomery slag (presumably the reason Drinker condemned the method in favor of furnace + fining) meant that it could potentially be reclaimed in a furnace charge. The stamping mill at Martha (where Moses Gaskill lost his finger after a month of working) could have processed the furnace's own cinder, and broken up massive ore from the bogs in lieu of, or in addition to, roasting; but one wonders if bloomery slag from elsewhere in the Pines was carted in as well.
The Martha diary for March 24, 1811 has the entry: "All gone well. Ore heap afire. Ore teams carting sand." The second sentence suggests a roasting operation to me; the diarist doesn't make it sound like a catastrophe (the sand is for molding).
My impression is that Gordon's caveat about needing ore of a minimum 55% iron content for successful bloomery smelting probably applies to bloomeries in general, which seem to have consumed higher-grade ore and of necessity produced fairly iron-rich slags. Given the general fussiness of the blooming process, I suspect roasting would have been necessary in general for bog ore fed into a bloomery forge in order to produce anything like consistent, quality iron, but this is speculation on my part. The simplest form of roasting would have been simpler than charcoal burning: just make a gridiron of logs, heap ore on it, ignite and allow to burn (no turf necessary)!
I know in the Piedmont and Ridge & Valley, old charcoal flats can be detected on LIDAR from their alteration of contour and field-checked by the detection of a charcoal layer in the soil; has this been done in the Pines as well? Presumably a roasting site would look similar but leave a mixture of charcoal and powdered ore somewhere in the soil.
Note that the high iron content of bloomery slag (presumably the reason Drinker condemned the method in favor of furnace + fining) meant that it could potentially be reclaimed in a furnace charge. The stamping mill at Martha (where Moses Gaskill lost his finger after a month of working) could have processed the furnace's own cinder, and broken up massive ore from the bogs in lieu of, or in addition to, roasting; but one wonders if bloomery slag from elsewhere in the Pines was carted in as well.
We've discussed forge slag and its high iron content on this site before, but while poking around Upper Hampton Forge the other day, I got to wondering why the forge slag wasn't brought back to the furnace to be used again.