So, I read a while ago several threads about making iron objects/blades from blood. In my conworld there are giant predators that would, according to my calculations, have enough blood so that 12 of them would make a decently sized sword (though that was counting the organs and all — would go up to 24 with just haemoglobin). This would mean that regular/anniversary hunts for such giants could lead to enough blood being stored for a royal (or very high born) person to have a sword forged for when they become an adult. I'm going off the basis that they are made aware by someone that there is iron in blood but that this person doesn't really influence their tech at all.

So the question is: how would you go about — with a people that barely are at the iron age — extracting iron from blood? I understand you would have to boil off the liquids from the blood and then turn it to ash but if I understood correctly the most tricky part is to decompose the haemoglobin and release the iron. So, with as much precision as possible, what process would be needed to properly extract the iron in order to make it into workable slugs? Would simply heating it all up degrade the haemoglobin enough or not?

Agrajag commented that centrifuging the ash and then recovering what is at the very bottom would give what I assume to be iron oxide (since they then advised that chemically reducing the powder would be needed, adding it needed to be mixed with equal part powdered natural graphite or ground charcoal and heat in the absence of an air flow). So: how hot would it need to burn to get the right type of ashes? How fast would it need to spin to get the iron to fall? And could this be replaced by some sort of decantation? And finally, is it needed to have graphite/charcoal, especially in equal parts, or is it like iron oxide/ore where you'd need at least a bloomery if not an actual blast furnace to change it to workable iron? And so would any kind of fuel work? I'm thinking of bamboo being used for wootz/damascus steel.

Thanks a lot!

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    $\begingroup$ Spilling blood into a fire sounds like a step towards inventing black pudding, not a new metal source. It isn't obvious that it is even possible to extract pure metal using ancient techniques from so much dross without a decent amount of chemistry to purify things first. $\endgroup$ – Starfish Prime Apr 11 '19 at 19:46
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    $\begingroup$ This question has inspired me to make some crazy tyrant that has made a sword forged from "blood iron" 'donated' from his enemies. $\endgroup$ – Celestial Dragon Emperor Apr 12 '19 at 3:15
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    $\begingroup$ @Nierninwa I was wrong in my calculations because I used Serum iron figures which do not include hemoglobin. $\endgroup$ – Alexander Apr 12 '19 at 22:24
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    $\begingroup$ VTR: the edits make the question a worldbuilding question. Especially since we're focusing on an iron-age civilization. $\endgroup$ – JBH Apr 12 '19 at 23:12
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    $\begingroup$ Agree with JBH, the edits to clarify the question make it definitely on topic now (and a very interesting question). You could still trim off a little fat to make it easier to read (really all the story-specific context you need is "I have an iron age civilization who was taught how to make weapons from the iron in giant blood") but I'm a critical offender in that regard myself, so can hardly judge, lol. Thanks for the fix +1 from me. $\endgroup$ – MarielS Apr 13 '19 at 1:14


The royal alchemist, in his time away from trying to reproduce Greek Fire or trying to find the secret of immortality, was following orders of the King in trying to create gold from base metals and materials.

They reasoned that blood had special properties of giving life (if you lose all yours you die) and must be, in some fundimental way powerfull - maybe it could hold the secret.

So, very much the way phosphorous was discovered (by mucking around with quantities of urine), the alchemists, seeking the phillosopher's stone discovered iron in blood.

The process goes something like this (a chemist is welcome to correct this):

  • Boil the liquid off the blood.

  • Burn the residue to ash.

  • Mix the ash with water and spin very fast (see centrifuge).

  • Collect the solid residue at the very bottom of the stuff that's in the bottom of your flask.

  • Chemically reduce (mix with equal part powdered natural graphite or ground charcoal and heat in the absence of an air flow).

When you cool this powdered mixture you should be left with something that can be separated out into good and slag using a lodestone. Then it should be just a question of hammering it into a workable slug (see cold-welding).

This could indeed indirectly result in the alchemist recieving gold and becoming immortal in reputation, so partial success at least.

  • $\begingroup$ That's an interesting idea! Although I am not sure how advanced they would be and how much of an idea of alchemy they would have… but why not! $\endgroup$ – Nierninwa Apr 11 '19 at 21:22

No it would not

you have several problems

  1. you will need gallons of blood to make anything describable as a nugget.

  2. higher oxygen concentrations will work against you since it means the blood needs less hemoglobin.

  3. 1200C is to low to smelt iron, you need something closer to 1600c. At 1200c iron is not even enough to forge iron much less smelt it.

  4. putting blood on a hot rock and burning off the water will make a sludge reminiscent of crude oil, heating it further will produce ash, and that's if you managed to collect it the evaporating blood will be energetic enough to scatter the few stable contents those temperatures are high enough to get the leidenfrost effect.

  • $\begingroup$ Ah, fair enough. I mean, then again, I'm most likely to stay around 22% so that wouldn't be a huge difference to now. Also, I guess accidental discovery by dropping blood on a fire wouldn't work. And sure, you would need a lot. I'd need something like 43 litres for 35 grams. But maybe some accident a smith would have could clue them in? Again, I'm not clear on the specific processes needed to recover iron from blood. $\endgroup$ – Nierninwa Apr 11 '19 at 21:25
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    $\begingroup$ keep in mind scholars figured out there was iron in blood only in the 1700's by analysing blood ash. so basically you are out of luck until about the same time they invent a steam engine. The iron in blood is just too scarce and hard to get at compared to what else is ino it. Basically people need to already be investigating chemistry. $\endgroup$ – John Apr 11 '19 at 21:36
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    $\begingroup$ On the other-hand people did stupid things to swords for various superstitious reasons since forever, they will not get any iron but you can easily have them dipping the swords in the blood for mystical reasons. Real humans did things equally pointless. $\endgroup$ – John Apr 11 '19 at 21:41
  • $\begingroup$ It doesn't have the same… importance to it though. Having to hunt down THIRTEEN massive predators is an idea I liked… $\endgroup$ – Nierninwa Apr 12 '19 at 22:06

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