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While doing research, I stumbled across the alloy "arsenical bronze", in which copper is smelted with arsenic instead of (or in addition to) tin. This apparently gives you "a stronger final product and better casting behaviour" than ordinary bronze, but what interests me is the use of a toxic metal in an alloy that was used, among other things, to forge swords and axes.

Arsenical bronze doesn't have enough arsenic in it to be toxic, but it got me thinking. Poisoned swords/knives are common enough in medieval fantasy stories, but you'd have to keep applying the poison to them, and that's a pain. But what if, by using toxic heavy metals or their various alloys, you could forge a sword that is naturally toxic?

In other words, is it possible to create a sword with the following properties:

  • Can be forged using medieval technology
  • Has a blade at least 45cm (18in) long
  • Is durable enough to survive a swordfight without breaking
  • Is toxic enough that being cut by it will cause some kind of physiological damage. It doesn't have to be lethal, but it should be more harmful than just being cut by a regular weapon
  • Ideally does not slowly poison the wielder, so long as they refrain from touching the blade

Things I am willing to handwave or ignore:

  • Whether the necessary elements/alloys, or their toxic properties, were known or readily available in medieval times
  • Whether the person who forged the weapon would have been poisoned in the process

Since a few people have asked what the use case for this weapon is: I was thinking it would make a cool unique weapon for my RPG series (hence the "medieval" requirement). A toxic sword isn't particularly useful in a real swordfight, but in an RPG battle where powerful enemies could tank dozens or even hundreds of hits, suddenly it's a lot more handy.


I am aware of this similar question, but it's specifically asking whether you could use pure arsenic to make a toxic sword, and the answer is no (it's too brittle). I'm asking whether there are any alloys that would let you make such a weapon.

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    $\begingroup$ A swordsman who needs his sword to be poisonous isn't a very good swordsman. $\endgroup$ – cgTag Jul 14 '18 at 16:57
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    $\begingroup$ I would think almost by definition that any weapon which continues to deal damage beyond its initial wound would have to leave something behind, meaning that it would wear down with use, hence the need to continually reapply the poison. If the sword's material itself is what's being left behind, I'd think that sword wouldn't last very long. $\endgroup$ – Darrel Hoffman Jul 14 '18 at 17:16
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    $\begingroup$ It seems to me that a poisonous alloy would be more useful for poisoned arrows than for poisoned swords which the swordsman would usually instantly withdraw from the wound in order to continue fighting the same or another foe. But arrows are usually not withdrawn from living victims by the side that shot them, but instead are withdrawn by the side the victims belong to. That is why war arrows often had barbs so taking them out caused more damage to the victim. Thus poisonous arrowheads would remain the victim much longer and would be more likely to give a big dose of poison. $\endgroup$ – M. A. Golding Jul 14 '18 at 17:46
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    $\begingroup$ Steel is really poisonous. Stick a steel sword directly into your enemies stomach - see? Instantly poisoned. $\endgroup$ – Whelkaholism Jul 16 '18 at 11:17
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    $\begingroup$ If it were an enchanted sword that yelled out insults, it wouldn't have to leave anything physical behind to be toxic. $\endgroup$ – Ian MacDonald Jul 16 '18 at 16:00

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There's a lot of toxic metals. Most are toxic in fact (including iron technically, if you get enough of it). Almost all of them have issues though:

  • Mercury: One of the first metals many people think of when they are thinking of poisons. The problem here is quite simply that even those mercury alloys that are solid at room temperature (known as amalgams) are generally not hugely toxic (they were even used classically for dental fillings). In fact, most of the mercury compounds that are toxic are entirely non-metallic (see dimethylmercury for a particularly nasty example), and therefore not very good for swords. The fumes from mercury are, however, rather toxic (they're a slow acting neurotoxin), so maybe you could coat your weapon in mercury (though that would put you at risk too).
  • Lead: Is a very slow acting toxin, and does not lend itself well to usage for a sword. It's also not very readily absorbed by the body in pure form, with most of the toxic forms being salts (white lead for example) or organic compounds (like tetraethyllead). It's also not good for a sword, it's way too soft, and it tends to soften other alloys (steel with a high lead content has a significantly lower shear strength than steel without much lead in it).
  • Cadmium: Is also mostly a slow acting toxin. Most of the same issues that lead has for this usage are also problems with cadmium. The biggest difference is that it would be a whole lot more dangerous to the swordsmith to make a sword out of cadmium, because the fumes and dust are far more dangerous than those of lead. Interestingly, cadmium is rather corrosion resistant, so if you were to go with this, the sword would actually not need to be cleaned as thoroughly to keep it in good condition.
  • Thallium: Most people probably haven't heard of thallium outside of chemistry class as it's not used for much. It's located right between lead and mercury on the periodic table and is actually significantly more toxic than either. It's interestingly one of the few metals which are actually sufficiently toxic in pure form to be dangerous to handle and might work here. Unfortunately, it's not very practical for this because the swordsmith would most likely receive a lethal dose well before he finished forging the sword, and it's also very soft and has a low melting point (just like lead), which means that alloys incorporating behave similarly to those which incorporate lead. Somewhat notably, thallium and its salts were a favorite means of political assassination in ancient Rome.
  • Osmium: Like thallium, most people won't have heard of this one much outside of chemistry class. Osmium might be the closest to what you're looking for. It naturally oxidizes in air to form osmium (VIII) oxide, which is insanely toxic (concentrations so small you can't tell it's there can cause pulmonary edema and permanent blindness) and also sublimes readily (converts from a solid to a gas). Osmium is also the densest naturally occurring chemical element known to man, so anything made of it is heavy (good for a weapon if used right), and it's also rather durable too (it's used in small amounts in alloys for fountain pen nibs for this reason). The big issues here are that just like thallium, it's liable to kill the swordsmith well before he finishes the weapon, and, more importantly, the weapon would just as dangerous to the one wielding it as the intended target (because of the fumes).
  • Chromium and vanadium: Both of these are probably already in your steel in small amounts. Both of them have a number of compounds that are very toxic (vanadium more than chromium). Unfortunately, none of these compounds can be produced in a weapon (they're all salts in some way) in any way that wouldn't make the weapon significantly less useful (they would compromise the structural integrity of the weapon).
  • Nickel, copper, cobalt, silver, scandium, and yttrium: Similar story to chromium and vanadium, just not likely to be in your steel already.
  • Zinc: Zinc is actually an essential nutrient. Like most metals which are essential nutrients, getting too much is very bad for you. Overabundance of zinc in the body causes all kinds of nasty things, interfering with copper and iron uptake, destabilizing cholesterol levels, and acting as a mild neurotoxin with permanent effects. The problem with using it for something like this is that it's the ionic form, not the metallic form, that causes problems and is readily absorbed. In fact, most of its alloys that are actually practical for swords are pretty much entirely non-toxic. A pure zinc stiletto might be viable for this if you stab someone in the stomach (such that it ruptures the stomach), because stomach acid dissolves zinc, and the resultant zinc chloride solution is really corrosive, but such a weapon would effectively be a single-use affair.
  • Antimony and arsenic: Not technically metals, though they are found in measurable concentrations in many old steel alloys. Both of these are reasonably fast-acting toxins in their oxide forms and oxidize readily. However, proportionate to how much you can reasonably put in a sword the size you're describing without making the steel useless for a sword, it takes a lot to actually kill someone. They are however persistent toxins (that is, if you get a bit of arsenic or antimony oxide in your body, it's going to stick around for a long time), and do have effects prior to reaching lethal levels (they make the victim tired, because they interfere with energy storage in their cells).
  • Selenium and tellurium: Similar story to antimony and arsenic, except these generally aren't found in even the oldest steels, and the mechanism of toxicity is somewhat different.
  • Aluminium: Believe it or not, aluminum is actually toxic to most living things. It's unfortunately impractical for what you want for a lot of the same reasons that aluminum foil doesn't poison people, it forms inert compounds very readily (aluminum oxide is non-toxic and extremely unreactive, and forms readily in air), the metal itself isn't well absorbed by the body, and rather large amounts are needed to cause significant effects.
  • Beryllium: First off, beryllium is impractical for a sword, it's too light and brittle. There are some other issues with using it for this though, most notably that it's not really all that toxic in its pure form (you should be noticing a theme here by now) or when alloyed (beryllium copper is a good example of an alloy that might work for a sword, but it's generally considered perfectly safe), with the compounds being the biggest issue (except see below). It's also not easy to alloy with most metals, difficult to work, and, most interestingly, is primarily an issue in the form of dust (which has similar long-term effects on your lungs to asbestos).
  • Lithium: Lithium has similar issues to beryllium, but deserves separate mention form the other alkali metals because it also has some of the same issues that aluminum does (namely, it readily forms inert compounds).
  • Rubidium and cesium: Both of these are really nasty slow acting toxins if ingested in the form of water soluble salts (for example, chloride or nitrate salts) because the ions interfere with biological processes that normally use sodium or potassium ions. Both of them are really nasty explosives if exposed to air (they react with the moisture in the air just like potassium and sodium react with liquid water, just way more so). THey're also damn near impossible to isolate in their pure form by any means other than modern technology. Given these constraints, they're impractical for what you want.
  • Strontium and barium: Same issues as rubidium and cesium, except they're not really explosive in air.
  • Lanthanide metals: All of these are toxic to some slight degree. They also have physical properties that make them unsuitable for use as a blade and are insanely difficult to isolate (to the point that many of them were not isolated in their pure form until the later half of the 20th century).
  • Radium, uranium, and other radioactive metals: All radioactive, so they violate the requirement that it does not harm the user. Also, actual toxicity other than the radioactivity is not well characterized.
  • Polonium: Polonium is insanely radioactive. So much so that less than one microgram (one millionth of a gram, that's about 1/60th of the size of a grain of table salt) is enough to kill someone due to acute radiation poisoning. Handling it is dangerous to the point of being almost suicidal. It's also really rare and extremely unstable, so the likelihood of getting enough to do anything practical with in medieval times is essentially nil. Given all this, while it would be very effective, it's also highly impractical. I've mentioned it here separately from the other radioactive metals simply because it's so much more dangerous.

I've refrained from mentioning many of the transition metals above, as they're either not reactive enough to be meaningfully toxic (titanium, platinum, palladium and iridium), too hard to isolate or reasonably work with in medieval times (tantalum, hafnium, niobium, manganese, tungsten and all the ones whose name begins with 'R'), or are just plain impractical for a sword.

So, overall, you're not likely to find a metal that can do what you want just based on metal alloys. There is also the issue of exposure. Cutting someone does not allow for much exposure, because the blade is kind of supposed to remain in one piece without losing much (if any) mass. Even regular blades coated in poison are not particularly reliable in real life, as reliable delivery of the poison is still difficult even if it's a liquid.

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    $\begingroup$ Wow. This is as comprehensive an answer as I could have hoped to receive. I've heard of osmium but I didn't know it was that dangerous. I think you're right, that's probably as close as I'm going to get. $\endgroup$ – F1Krazy Jul 15 '18 at 0:32
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    $\begingroup$ An interesting fact wrt mercury, people used to swallow huge globs of mercury in quicksilver form to treat gastrointestinal blockages (and it worked, since the blob of mushy metal would help push anything out), and the worst that would happen is mild to moderate brain damage many years down the line, not instant death! $\endgroup$ – forest Jul 15 '18 at 1:12
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    $\begingroup$ I actually have to wonder about the radioactivity harming the user. Because of the inverse square law, you can easily have an amount of radiation that causes severe burns when extremely close (millimeters) but has negligible effect on the person wielding the weapon. The same could apply to alpha or beta radiation where the skin can protect from it to a large extent, but a weapon penetrating the skin would cause extreme internal burns. $\endgroup$ – forest Jul 15 '18 at 1:18
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    $\begingroup$ You missed a point about polonium. It's so radioactive that a sword cannot be made from it - the self-heating in a mass that size will cause it to melt. It would, however, have the canonical blue glow. Take that, orcs! $\endgroup$ – WhatRoughBeast Jul 15 '18 at 14:57
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    $\begingroup$ @WhatRoughBeast xkcd.com/1114 $\endgroup$ – Brian McCutchon Jul 16 '18 at 4:59
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In order for a poison to be effective, it has to be transferred into the target. If the source of toxicity is the metal itself, the sword could only work if with every blow you'd be leaving enough of the blade in the wound to deal meaningful damage.

That's even worse than dipping the blade in liquid poison before battle. Instead of running out of poison and being left with a regular blade, you'd run out of the poison AND the blade, being left with a subpar weapon.

On the other hand, as M. A. Golding said, a disposable blade like an arrow or javelin tip could be an application for a toxic metal. Unfortunately, for a something solid to be readily toxic, it has to react with blood, and if it does that it'll most likely react with air moisture over time, so your arrow tips would decay in storage. Still, not an improvement over surface-applied poison.

The problem with using metals as poisons to get them into the victim's body. Not just get inside physically, but biochemically. Gold here is an outstanding example: gold, in fact, is as toxic as you'd expect from a heavy metal. But it's so unreactive in metallic form that its bioavailability is pretty much zero. But gold salts (actual salts, like gold chloride) are dangerous. Similar (but less shocking) thing is with mercury. How toxic is a drop of mercury once in a lifetime? Hardly. You can play with it with your hands. You can swallow it and you'll crap it out. You can inject it and the worst it can do is mechanical vein blockage. Metallic, it doesn't enter your biochemistry fast enough to be deadly on exposure as short as you have in battle. Only after years of prolonged exposure you can get mad as a hatter. Compare that to dimethylmercury (organic salt): a single drop on a rubber glove clad hand and it's lethal exposure. "One of the strongest known neurotoxins."

Bottom line: toxic metal in a sword is dangerous only to the soldier carrying it. Just like any toxic solid.

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You don't need any special materials to make a toxic sword.

If you want a sword to be useful for as long as possible, you will make it out of an alloy that is resistant to oxidation. Oiling it here and there and keeping it in its scabbard go a long way into keeping the sword from rusting.

Now sometimes you have a bastard sword, and sometimes you have a bastard swordsman. If you don't take good care of a sword - or if it is just too old - the sword will become rusty. Much worse is someone who would be negligent on blade maintainance on purpose. Anyone who is cut or maybe even just scratched by such a blade will need a shot for lockjaw, a.k.a. tetanus. The rust itself does not cause the disease, but the bacteria that causes it loves rust.

Now remember, vaccines and antibiotics were invented way after medieval times. I've heard historians say that anyone that survived a battle in ancient and medieval times would likely die or lose a limb due to infections (not only tetanus). Cutting a fellow soldier's arm and cauterizing the wound with red-hot iron was a thing in some places.

So there... In ancient times all swords were toxic, but not in the way you probably were thinking.

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    $\begingroup$ Giving the enemy tetanus is like an eight week damage-over-time attack $\endgroup$ – Schwern Jul 15 '18 at 16:29
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    $\begingroup$ Pratchett used that one as well (unsurprisingly), in The Light Fantastic: "The jeweller had produced a very large and dirty axe, guaranteed to add tetanus to all the other terrors of warfare." $\endgroup$ – oliver Jul 16 '18 at 12:57
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The metals which are pretty nasty when present into wounds do not suit well for making a blade: alkaline metals like sodium can be really dangerous when in contact with water-based solutions, causing burns, but they are pretty soft.

The closest you can get is having a bladed with a rough surface (aside from the cutting edge), where you spread quicklime (CaO) before each battle.

Being highly reactive with water, quicklime would have a nasty effect when dispersed into the wound upon cutting the flesh of the victim.

When the blades clash during the battle would disperse powder of quicklime, which upon landing on the sweaty skin of unprotected fighters could also cause burns or irritation. But then your fighters cannot fight a la 300.

Quicklime was commonly used for building in middle age, and its reactivity with water was known.

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    $\begingroup$ If I saw a soldier in my unit spreading quicklime all over their weapon, I'd transfer to another unit. I would not want to be near that person when they start swinging, armor or no armor. $\endgroup$ – Schwern Jul 15 '18 at 16:25
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According to at least one science fiction authoring team, iron from meteors may possibly be radioactive enough to cause physical damage to people who touch it, but if it is, that damage would still be rather slow. So radioactivity is better reserved for justifying curses than powering death blades. Also, short of lead-lined armor, radioactive blades tend to hurt their wielders more than those they are wielded against.

Bacteria would be my go-to for creating a kill blade. With little more than a layman's understanding of modern germ theory, a warrior could brew up something really nasty using the dead bodies of his previous victims, then carefully contaminate the cutting edge of his swords. Again, death wouldn't be instantaneous, but in a medieval age, it would likely be guaranteed.

Alternatively, a skilled iron-smith could carve ridges into the blade's plains along the surfaces which will contact enemy flesh after the cutting edge has done its job. In those ridges, any number of fast-acting poisons, narcotics or psychedelic compounds can be stored.

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    $\begingroup$ Obligatory xkcd: Metallurgy $\endgroup$ – Theraot Jul 14 '18 at 16:17
  • $\begingroup$ Various unsavory types throughout history supposedly used human waste as a vector for bacteria, exactly as you suggest. Mostly this led to the wounds getting infected, which greatly slowed healing if it didn't kill you outright. It's not by any means a fast death, though. $\endgroup$ – Cadence Jul 14 '18 at 20:02
  • $\begingroup$ "Iron from meteors can be radioactive enough to cause physical damage to people who touch it": Can you provide a source for that? A quick google doesn't turn anything up (and a few sources (eg meteorite.com/meteorite-information/meteorite-facts) saying "They pose no danger at all" $\endgroup$ – Martin Bonner Jul 16 '18 at 15:02
  • $\begingroup$ @MartinBonner, I have no scientific reference to support that claim but I have encountered it in mainstream fiction, most notably in RipTide by Lincoln Child and Douglas Preston. As your reference is more authoritative than mine, I will modify my answer. $\endgroup$ – Henry Taylor Jul 16 '18 at 15:41
  • $\begingroup$ I'm not really seeing a lot of answers here that seem much more effective than just using a sword in the normal way would be. $\endgroup$ – T.E.D. Jul 16 '18 at 18:25
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I don't think so,

So far, the answers all focus on additives to a standard sword (poisons, additional toxic metals that have to be added or replaced to keep the sword toxic.

Metal Sword

Your question seems to be asking, though, if a sword in and of itself can be a toxic weapon, without having to make and add poisons or heavy metals. Metals that are good for making swords (bronze & iron) aren't in and of themselves toxic; toxic metals known in medieval times (mercury, arsenic, lead) aren't really toxic enough immediately after battle for them to help much. Possibly if you were able to stab someone sixty or seventy days in a row with a lead sword, some bits might get lodged in his body and cause lead poisoning...

Not very practical!

Stone & Wood Swords

Useful toxicity is a strong province of biological agents. Some woods can cause reactions, but really aren't strongly toxic enough in and of themselves to be the weapon you're looking for. Perhaps if you made a sword from fresh manchineel wood. The sap is extremely toxic.

Stone is not terribly toxic either, though compounds that are (lead or arsenic compounds) don't make for very sturdy swords!

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    $\begingroup$ A thought, piggybacking off your wooden swords idea. A Macuahuitl with thin blades of lead in place of obsidian. The blades shatter and get mixed into the cut wounds, poisoning the victim if they can't get the shards out after the battle. Downside is you'd need to periodically replace the lead. $\endgroup$ – MetalJimmor Jul 14 '18 at 23:56
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    $\begingroup$ @MetalJimmor somewhat doubtful of the effectiveness - people have been shot with bullets containing lead for years and actual lead poisoning has been a negligible factor in GSW lethality. See Austin Hemmelgarn's commentary on lead in his answer. $\endgroup$ – KerrAvon2055 Jul 15 '18 at 1:51
  • $\begingroup$ @MetalJimmor surely the lead would just bend and not shatter $\endgroup$ – Chris H Jul 17 '18 at 8:42
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It's not realistic as poison in general is not very realistic for being useful on a sword. Poison ist for maliciously, and covertly, murdering someone. It's not what you bring to a sword fight.

You would need a very active nerve agent to have any noticeable effect (which is not available in a medieval setting). But then, you had better not accidentially scratch yourself. While poisonous metals exist (abundantly), they are not nearly toxic enough to be useful.

Even coating a sword in curare would not be of much help, as it will take minutes before the poison affects the victim significantly enough to be of advantage. Inhaling or injecting a poison intravenously is not the same as having some traces of poison in a scratch. Also note that bleeding will transport poison out of the victim's body, not into. So, the applicable dose will be rather not so awesome.

Practically, if you are the only one with a sword, then killing the other person is no challenge, no poison needed. If, on the other hand, both of you have a sword, then the other person dying from poison 2 hours later is not much of an advantage. Either you have killed them anyway, or they've probably killed you. In one case, it didn't help, in the other you wouldn't know.

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  • $\begingroup$ Can I have poison arrow frog swords? $\endgroup$ – Joshua Jul 16 '18 at 16:19
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    $\begingroup$ @Joshua: That would probably work. Batrachotoxin is arguably as good as you can get, if the sources that allege near-instantaneous paralysis are true (though not very likely to be honest, local pain and paralysis is more likely). The main problem will be finding the frogs, the preparation, and the general danger (to the wielder) involved with such a sword. But it wouldn't be a poisonous sword, it would be a poisoned one. $\endgroup$ – Damon Jul 17 '18 at 6:47
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Since according to the other commenters, toxic swords do have a lot of problems, I suggest leaving the toxicity to other things, like infections. In medieval times wound care was pretty bad and often lead to infections - often, but not always.

So why not increase your swords chance to inflict infections? A rough cut rather than a clean one is more difficult to treat and has a higher chance of infection - a somewhat dull sword for example. You could also use multibladed weapons (imagine two swords duct taped together side by side). A serrated blade would also work, especially if the teeth are bent at different angles. If you make the sides of the blade (but not the cutting edge) rust a bit it would be quite an unpleasant experience for anyone getting cut.

In addition to the high risk of a really bad infection, they would also have a higher chance to cause the enemy to bleed out.

While similar to applying poison, you could also dip it into dirt, mud, excrement or simply a dirty puddle to increase the chance of infection - this would be made even worse with a rusted blade.

With this, a scratch of an unpoisoned blade has a really high chance of causing death after a couple of days.

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Dissimilar metals. Connect them with a salty liquid (eg blood :) ), and you get a (low voltage*) battery. Which will also send metal ions into that salty liquid. Depending on the kind of metal ions being washed into the bloodstream that way... Electricity in a wound/in the bloodstream is also usually not a healthy thing (and rather painful).

You would need an insulating layer though (eg glass, stone) ... glass to metal sealing is technically done nowadays, of course it would be quite a feat with medieval technique...

*a blade design that keep wet across several "cells" after a strike, but connects the opposite ends of that chain could be quite effective here...

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Perhaps we can expand the definition of "toxic" to include other forms of harmful long term effects from a short term fight. Instead of strictly poisoning the target, we could instead infect the target with some form of pathogen.

Take, for example, Tetanus. Though it is recognized from antiquity, it would not really have a cure or treatment in medieval times, and it would be a crippling affliction with a ~10% mortality rate.

Tetanus works fairly well specifically because it poses lower risk of infection for the wielder as the risk of infection mostly comes from a wound caused by something with the Tetanus bacteria on it, rather than simple proximity to the source. But, of course opening up this course of action leads to many possible pathogens that we could use.

Another bonus for this form of "toxicity" is that because the vector is a living organism, it can reproduce itself and thus lessen the need to "reload" the pathogen (in the case of bacteria, though viruses could reproduce themselves given a suitable environment)

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