I'm an amateur but I've read a fair bit on metallurgy. I cannot see
how sea shells could impart carbon which is what you are doing when you
case harden. Rather, I would think that the sea shells acted as some
kind of basic flux since they're made of lime, which is basic.
On the other hand, according to my old blacksmithing books, items were
case hardened by placing them into an iron box in which they were
surrounded by bone fragments or even powdered charcoal. The box,
containing the parts, was then placed on the forge fire. Once the fire
ignited the contents of the box, and after it burned out and cooled
down, the case hardened parts were removed.
I fail to see how sea shells could be used for this purpose.
But the day isn't over. So there's yet time for me to learn something
re: the seashells
Calcium carbonate, that's the bulk of seashell. Seashells make limestone,
given enough time and pressure. The primary purpose of the shells was as a
flux to bind the mass together, but the carbon may have enhanced the ferrite
into a crude steel by 30 or so points. Usually, bloom furnaces didn't get hot
enough to get to force the large uptake of carbon that we see in modern pour
furnaces. Charcoal just doesn't have the kick that coke does.
Pack carburization; burying apart in coal dust and baking it at the back of
the fire, takes advantage of the 'carcon into solution' phase. As the temp
comes up in the box, the part is bathed in a carbon monoxide-rich reducing
environment, and carbon soaks in from the surface over time. Take iron
strips, pack them in carbon dust and bake them for a few hours at medium
red. Then weld them into a billet, make a sword. What you have is a high
carbon skin over a low carbon core on each strip. Higher carbon lowers the
fusion point temp, so the strips weld easily with less fuel. It was fuel
that was the point of diminishing returns in antiquity, trees only grow so
Why swords had names:
Think about just how many people were in line for their cut of the
swordsmith's price. The smith, his apprentice, the two or three shop drudges,
the charcoal burner and his crew, the smelter and his crew, the forresters,
the teamsters (yeah, even waaaaay back then), the miners... the line's
getting long. This many people sweat over somthing and it 'aquires' a
personality, seemingly by osmosis. YMMV.
Might be that the shells bring Oxygen as they bake and fluxing it inside the
Hard to say. Maybe the flux by itself keeps the carbon from burning off.
The reverse of my first thought.
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder
On Thu, 17 Nov 2005 19:34:33 -0600, "Martin H. Eastburn"
When you heat calcium carbonate (limestone, shells) hot enough, CO2 is
liberated leaving CaO, or quicklime. Hit that with H2O, and you get
Ca(OH)2, or slaked lime. Leave that around long enough, and it'll
absorb CO2 out of the air and turn into calcium carbonate + H2O. I
don't think CO2 will carburize anything.
Lime is a useful material for many purposes and has a long history of
production by burning calcium carbonate rocks in a lime kiln. Where
oyster beds were found on the shore (the "sea shells" most likely to be
found on these quantities) then they represented a high quality source
of calcium carbonate and were often used instead.
There's a nice description of this in the T'ien-kung k'ai-wu (A 17th
century Chinese compendium of technical knowledge - the Dover reprint is
well worth reading) It also states [on oysters] "After a long period of
time the inside melts to form a fleshy lump, called oyster meat, which
is delicious to the palate".
Lime may also be used for the smelting of iron. It's little used these
days, as a blast furnace is big and hot enough to "be its own lime kiln"
and so the "lime" is added as the raw limestone instead. This has both a
fluxing effect and also takes part in the reduction chemistry that
reduces iron ore to iron.
Lime isn't used as a flux when smithing though. Even forge welding just
isn't a hot or isolated enough process to use it as such, so something
more active like borax is used instead.
Useful though it is, you can't case harden with lime. You need a carbon
source and a reducing agent. Depending on how you do the process, you
might need just the carbon source.
There are two ways to do case-hardening. One is to get a sealed iron
box, pack it with carbon-donor and then heat it to a dull red in some
sort of furnace. then leave it there for a few hours. This is the best
process, as used in old industry.
Historically the favoured carbon source for this was finely chopped
hooves or rawhide trimmings from a tannery. Bone has very little
available carbon in it, so isn't useful here. Tanned leather might work,
but a leather tanned with metal salts (most of them thee days) might
cause its own problems. Charcoal can also be added (but not entirely).
The simpler process (the only one that's really workshop-practical) is
to take a tin of cold carbon-donor, heat the end of your new
chisel/whatever and stick it into the magic powder. leave until coold
down, then repeat a few times. The problem is that because it's a cold
and rapid process, it's very difficult to get the carbon on-board. You
need some additional chemistry, typical nitrogen compounds including
cyanides. Using plain old charcoal just isn't going to do a thing.
Really, you need to find a tin of commercial Kasenit to make this work.
Doing it from hoof and horn first principles is strictly for the
Industrially, case-hardening is now done with liquid tanks of
ferricyanides. Better engineering through chemistry.
He should find a horse or cow instead. _Much_ more to use!
If he's a smith then he's probably a closet Norse pagan and is hiding
his fingernails away so that Naglfahr "may be long in the building and
low in the draught" 8-)
Cats have nine lives, which is why they rarely post to Usenet.
I understand that, but wasn't bone charcoal used to case harden?
>>Using plain old charcoal just isn't going to do a thing.
Why not? Powdered charcoal is ...Carbon!
Modern science and Kasenit are great, but do tell howcome soaking a
part at red heat packed in charcoal dust anaerobically just won't work?
"trims toenails often"
Oooo... good questions. :)
I'll see what I can find out in this corner of the world.
First bones are protien with "added minerals for stiffness;)".
Don't know the weight percentage but the first statement is true
IMO even if they are only 1% protein. You can take calcium out of
a bone but you can't take the protein out and still have a bone.
Calcium phosphate is the main -mineral- in bones (so said my 8th
grade health teacher;)
If: pure carbon doesn't soak into steel then it's obvious that the
carbon needs a "push" or maybe an "activator". Cyanide seems to
supply one or both of those to the carbon. What else can/will do
that? I have no idea. :/
Ok, that's what I fiNger.
Just happen to have checked out from the library Metals Handbook
Volume 4 "Heat Treating"...
The book's articles are all about "gases".
One of the interesting sections tho is on "carbonitriding".
Nitrogen and phosphorus act like carbon and boron when it comes to
hardening steel two of the three together is pretty powerful stuff.
Metallurgy math: 1+1=4. :)
The old-timey;) methods packing the iron in animal products at high
heat sounds like carbonitriding at least, to me, don't it you too? :)
The depth of carbon-case, in 16 hours at 1675F can be .040" and get
I've always had the impression that's what the "real damascus steel"
was... thin layers of iron with carbon (and nitrogen?) soaked into
the surfaces of those thin layers (part way?) and since that was the
outside, is later, the weld, and ends up on the inside so the welds
are thin layers of high carbon steel. ??
I read where the iron they were getting from India had a little bit
of vanadium naturally alloyed into too?
I see a hundred fires going all at once, burning day and night with
various levels of partially finished billets soaking in fires with
every spare animal product avaiable in those fires including shit.
Soak the outside surface in a carbon+nitrogen rich fire for a day
and when retrieved, fold it, weld it and hammer it out (fold it
the other way hammer it out again?) then it goes back into the
stinky-ass fire to get re-charged with the "strength of fire" for
a day or so.
The billets are brought to the "blacksmith" and his crew of two or
three hammerers, the blacksmith would also be acting as a foreman
positioning the billet on some sort of anvil and making decisions
about how to go about it and when it needs re-heating etc.
Certain hammerers become blacksmiths.
Fire-tenders, billet-trackers at the fire, billet-couriers,
blacksmiths (acting as foreman with a hammer-crew), finishers
and handle-makers etc.
What do you think?
See something else to add? :)
Alvin in AZ
Charcoal from all sources was used, but needs to be mixed with an
"energiser", usually barium carbonate. Steel can't be hardened by
carbon alone, as this is effectively immobile. The active carbon is
transferred in the form of gaseous carbon monoxide, generated by the
breakdown of the carburising compound and the oxygen packed into the
sealed box. This takes place with pure carbon, but unworkably slowly.
Adding an easily decomposed carbonate such as barium carbonate breaks
down to BaO + CO2 and this encourages the reaction
C (from the donor) + CO2 <-> 2 CO
increasing the overall abundance of CO and the activity of the
If it's anaerobic, it's going absolutely _nowhere_. Although the box is
sealed, there is plenty of oxygen inside it. This is re-circulated
through the CO cycle, but it's vital. The sealing is necessary to stop
the CO either leaking out, or being oxidised to CO2 by excess outside
Bone contains some carbonates, but is mainly calcium phosphate (as
hydroxy-apatite). This doesn't have the beneficial effect on encouraging
CO production and it can also supply phosphorus as an impurity into the
steel alloy. Bone can certainly be used, but not entirely.
The most effective nitrogenous compounds have more complicated chemistry
which I can't claim to understand. AIUI, they can also produce some free
cyanide CN as well as CO, which is a more efficient carbon transport.
This is a different reaction from the liquid cyanide salt baths, which
operate with sodium cyanate (NaCNO). This is noted for a fast
carburising action, but a much thinner skin.
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