The direct process bloomery furnaces we will be building really need at
least 50 % Fe content to the ore to function. Closer to 60% would be a
lot better. This is pretty pure, as modern mines usually run closer to
25 - 30% as a viable ore body. This means it may be hard to find a
usable ore at an existing or abandoned mine.
Sauder & Williams are using ore from Colonial Era workings in
Virginia. They manage to find good ore because these were deposits
deemed too small / too remote for even the technologies of the late
1700's. So looking for long abandoned
*small* workings might be a clue.
Your black, heavy ore? Is it magnetic?
This might suggest a deposit containing Fe3O4?
Lee Sauder suggests a very rough 'field test' for Fe content. Take a
sample that looks good / typical. Pound or grind it to small fragments
(sand sized). Place about a hand full in a glass jar and weigh. Fill the
jar with mild acid, something like muriatic / hydrochloric (pool
chemicals from the hardware store) or sulphuric (battery acid). Leave
this overnight, shake the jar now and then. Pour off the liquid and
refill the next day. Repeat until the acid stays clear. Now pour off the
last liquid and let the contents dry in the sun a couple of days. Weigh
the jar again.
The difference in weights should be the amount of iron removed, this
gives you a ball park number for your purity.
It would be great to smelt using a locally available (?) primary bog
iron ore.
Problem there is twofold:
1) Even if bog ore is present, actually finding an actual deposit area
can be pretty difficult.
2) Even if the geography allows for a deposit, is there enough ore
available for an effective smelt. (see below)
For the SSW project, it would be great to attempt a smelt using that
distinctive Macaulyite ore. Again, you will have to advise if you can
get enough of the material to allow for this. (see below)
As a back up, there are two possibilities I can see:
1) Source a suitable quantity of industrial taconite pellets.
With the long history of industrial iron production in Scotland, I would
expect this would not be massively difficult. Perhaps contacting one of
the (still existing?) industrial operations?
Usually even an abandoned modern plant has tons of this stuff piled /
spilled around. Given that we would be looking for at best a couple of 5
gallon pails of pellets, gathering up enough is more a problem of
getting to the source.
This also might suggest attempting to make some kind of sponsorship
arrangement with an existing corporation? At the least it would be
donation of taconite, but maybe this could be expanded into some project
funding? Even covering the cost of the charcoal for the project would be
a massive help. (Something like "'Scottish Steel' - From the Past and
into the Future") I certainly don't have any problem promoting a local
company / business who makes a significant contribution.
2) Making up a suitable ore analog.
This will require sourcing a local / regional pottery supplier. The raw
iron oxide, both red (Fe2O3) and black (Fe3O4) should be available as 20
kg amounts. We could easily at least roughly duplicate the components of
the Macaulyite by adding other oxides. The primary consideration there
would be cost, and to a certain extent the time required for the drying
of the mixed paste (?)
Any given smelt attempt will require ideally 20 kg of ore as a working
amount.
My experience with this size / type of furnace is that at least 8 kg is
needed to basically establish the working environment inside the furnace
itself, the slag bowl system. Any amount of ore
*over* that 8 kg then
goes into the developing bloom.
The experience here is that given a suitable ore, 20 kg input should
give something in the order of 20 % + return as bloom.
This yield rises sharply as you increase the amount of ore used. Also
because the furnace system is established (heat and slag bowl), there is
a big efficiency increase with larger volume ore additions towards the
end of the working sequence.
However...
Remember the limits of manpower (and skills). As the blooms get larger
and larger, they become significantly more difficult to work. There is a
real limit to the ability of human hands to effect larger masses of
metal.* (Admittedly, with enough skilled strikers, even the largest
blooms possible via these small bloomery furnaces
*can* be compacted and
forged. You do have to be honest with yourself - how many skilled hands
are realistically available?) Despite the improvement in yield /
efficiency, this manpower gap is why at Wareham I tend to aim for
smaller blooms - in the 3 - 5 kg range.
* Although only a very (!) rough way to think about this is :
Force applied by a hammer is more or less a multiplication of hammer
mass times swing velocity.
Control of the hammer declines with the weight of the head, modified of
course by the skill and body size of the worker.
All this combines to produce a real limit to heavy a hammer any
individual can be effective with - and how much force they can produce.
The bloom mass itself has a resistance to forming. Very (!) roughly this
can be thought of as closer to the
*cube* of the volume (thus also the weight).
So a 5 kg bloom may take something closer to six times the amount of
hammer force to compress and shape it over a 3 kg one.
(Note - this is only intended as a rough ball park estimate - I'm really
not sure what the exact physics is here!)
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