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Pieter B.





Joined: 16 Feb 2014
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PostPosted: Thu 05 Jan, 2017 12:11 pm    Post subject: Did larger blooms result in better quality steel?         Reply with quote

I often read that increasingly larger bloomeries from the Early Medieval Period to the 16th century produced higher quality steel. Is the steel from a 100 kilogram bloom better than that of a 10 or 2 kilogram one? Is there a metallurgical process that makes larger blooms yield better steel or did smelters simply get better at their job? Alternatively could it be that an increase in steel production across all spectrums of quality simply meant that there was more higher quality steel to go around, or is the claim that steel got better unfounded?
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Mark Moore




Location: East backwoods-assed Texas
Joined: 01 Oct 2003
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PostPosted: Thu 05 Jan, 2017 4:17 pm    Post subject:         Reply with quote

Since no one else has answered you, I will at least reply. I've never forged a bloom, so I don't have much knowledge on the subject. But....It seems to me that most everything you said would basically be correct. It would also seem to me that the larger the bloom, the larger a piece of steel it would render. Therefor, having more to work with should be easier to get out the imperfections. Like I said...that's just the way I see it, fwiw. Happy ...McM
''Life is like a box of chocolates...'' --- F. Gump
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Peter Spätling




Location: Germany
Joined: 07 Nov 2015

Posts: 117

PostPosted: Thu 05 Jan, 2017 4:27 pm    Post subject:         Reply with quote

Bloomery is a really complex topic. As I'm going to make the steel for my harness myself I've been reading a lot recently. As well as get in touch with experts on the field. One of them would answer your question with a simple yes. Bigger blooms are more homogeneous, cleaner and contain material that can be forged better. Now what is a big bloom? I say a big bloom starts at 100kg. I guess due to the size and energy involved factors like the surrounding temperature and moisture lose in value. I don't know how the size of the oven affects the slag. When you run big ovens you need to run them longer, you are not done after 8 hours, but maybe after 40 hours. (That 's just an example, the time it takes depends on the ore, the amount....) As the fire burns longer you have more carbonisation and get more steel, rather than iron.

Also important is the ore you use. Phosphor is shit, this makes your steel really brittle. However phosphor can be found in nearly every limonite. Sulphur makes your steel brittle as well, but with weathering and roasting followed by abrupt cooling with water the sulphur content can be reduced.

A big advantage a larger bloom definitely has is that you don't have to rework it as often as smaller pieces. You can start compressing it when it 's still hot. Divide it into smaller pieces, while it 's still hot, and even rework those to some degree. Before you have to start reheating and forge welding the pieces of bloom. So you lose less material.
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Peter Spätling




Location: Germany
Joined: 07 Nov 2015

Posts: 117

PostPosted: Fri 06 Jan, 2017 4:18 am    Post subject:         Reply with quote

you should also keep in mind that the construction of bloomerys changed over time. Not only did they get bigger but the form changed as well. A tatara for example aims for high quality, while some European bloomerys were just meant to get as much iron as possible. The tatara you can see in the video burned 56 hours, was filled with 1,8 tons of magnetite and 4 tons of charcoal, the bloom weighed around 400kg and was of excellent quality.
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