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In my setting there's a lack of sulfur, simply put. Don't ask for the specifications, just assume that whatever amount there is, it is likely better off used in dietary supplements for the shortage of it.

Without access to this, what other propellants would humans use?

If possible, I'd like to know how effective those would be compared to gunpowder.

Edit for context: I am most concerned about the pre-industrial period. I appreciate those telling me about railguns and superheated water, but you need to walk before you can run and I want to figure out what everyone's doing for the 500-700 years before contemporary science makes those plausible.

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    $\begingroup$ ??? There isn't any sulfur in the projectile propellants used in guns and cannon. There has been no sulfur in the propellants used in firearms and cannon since about 1900 or so. And guncotton was discovered in 1846, 177 years ago. $\endgroup$
    – AlexP
    Commented Jan 28, 2023 at 18:29
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    $\begingroup$ @AlexP I'm assuming the question is asking about the development of gunpowder. Of course most weapons now are sulfurless, but had we not had sulfur-based firearms it's unlikely that we would have the weapons we have now. So I'm interpreting the question to mean, for a society at the technological level of the 1300-1400s, the next best thing. I may be wrong though. $\endgroup$
    – dreamforge
    Commented Jan 28, 2023 at 19:10
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    $\begingroup$ I hear that things vaguely resembling bullets can be propelled with taught cords attached to wooden or metal arcs which are flexed to build up energy... It's difficult to imagine, but weapons could likely be constructed using such a principle! $\endgroup$
    – Jedediah
    Commented Jan 29, 2023 at 3:40
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    $\begingroup$ Just to pedanticise, but eggs already contain sulphur. When they go rotten, the sulphur is converted into different, malodorous compounds. But you can't generate an element from nowhere, at least not without some very complicated atom-smashers. $\endgroup$
    – Greenaum
    Commented Jan 30, 2023 at 0:13
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    $\begingroup$ Does this answer your question? Chemical propellant free automatic weapons $\endgroup$
    – JBH
    Commented Jan 30, 2023 at 16:44

14 Answers 14

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Gunpowder with a different ignitor than sulfur.

A primer on explosives for coal miners. US Geological Survey Bulletin 1911

snip from primer on explosives

The heavy lifting in gunpowder is done by charcoal (the fuel) and potassium nitrate (the oxidant). Sulfur is in there because it is easily ignited, and it then ignites the charcoal.

In your sulfur deficient world people use different accelerants. Distilled alcohol is a common one, and alcohol in this role is sometimes doped with turpentine. Long term gunpowder storage is in glass bottles or tarred kegs. For cannons, glass bottles of gunpowder in alcohol are broken into the cannon or hole before wadding and ball, or powder is scooped out of the keg and used as a wet paste. For rifles the gunpowder is parcelled out before expected use into waxed paper envelopes. The alcohol evaporates from these over a week or two.

I am very pleased this question led me to find the primer on explosives for coal miners linked above. I love the way they wrote in 1911.

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    $\begingroup$ Alcohol does a crummy job of igniting black powder. As a kid, I used to make black powder for fun. I tried all kinds of things besides the encyclopedia recipe - including soaking the black powder in alcohol and igniting. The alcohol burns off first, drying the powder. The powder didn't ignite. The dried lump of powder could then be lit, at which point it burned better than powder that had been mixed dry. $\endgroup$
    – JRE
    Commented Jan 30, 2023 at 9:20
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    $\begingroup$ @JRE Alcohol is actually used in fireworks production to clump together black powder into colored charges. $\endgroup$
    – Blackclaws
    Commented Jan 30, 2023 at 10:10
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    $\begingroup$ Not sure alcohol or terpenated alcohol is a good choice here, but other low-ignition substances exist as well. Also, charcoal and potassium chlorate, sugar and chlorate, and a number of other combinations have been used in the real world as gunpowder replacements. $\endgroup$
    – Zeiss Ikon
    Commented Jan 30, 2023 at 19:09
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    $\begingroup$ I am pretty sure one could ignite non-sulfur blackpowder with red hot iron rod. Also non-sulfur blackpowder was used at leas from ~1800 - in shrapnel charges, as it was less likely to ignite from shot acceleration and consequent friction between shrapnel balls. $\endgroup$
    – Vashu
    Commented Jan 30, 2023 at 22:38
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    $\begingroup$ Maybe magnesium powder would be a suitable stand in for sulphur. That ignites pretty readily. $\endgroup$
    – egeorge
    Commented Jan 30, 2023 at 23:15
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I present you a real weapon used in real wars, made in 1779.

The Girardoni air rifle.

A Girandoni System Austrian Repeating Air Rifle, Circa 1795, believed to have been taken on the Lewis & Clark Army Corps of Discovery Expedition 1803-1806.

It was not merely an experimental curiosity, it was mass-produced and was in active military service for decades. It had a much higher rate of fire than muskets, and although less powerful, it was still lethal at the ranges typical musket engagements were fought at.

The downsides were that it was much more maintenance-heavy and expensive, so they went back to traditional gunpowder after a few decades of use, because it was much more practical to have cheaper guns any soldier could repair in the field, than having delicate and complex weapons which required specialized training to maintain.

But with gunpowder lacking completely or in extremely short supply, I can't see any reason against a more widespread adoption of these guns.

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    $\begingroup$ +1 one for the Girardoni. Lewis and Clark had one in their expedition. It's ability to shoot many rounds without recharging impressed the natives (who were well acquainted with gunpowder rifles) $\endgroup$ Commented Jan 30, 2023 at 10:38
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    $\begingroup$ The big problem with the Girardoni rifle is that the rate of fire is very "bursty": it could fire 30 shots in the same time it took a musketeer to fire twice, but it then took half an hour to re-pressurize the air tank. $\endgroup$
    – Mark
    Commented Jan 31, 2023 at 1:28
  • $\begingroup$ @Mark in Musket warfare that could be a massive boost though if used correctly. Mow down the first rows of the enemy formation and then pull a tactical retreat (or be replaced by a second group) $\endgroup$
    – Hobbamok
    Commented Jan 31, 2023 at 10:05
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    $\begingroup$ @Mark : the same could be said for a modern soldier if you only gave him an assault rifle but no spare magazines. Btw. the average soldier in the Napoleonic times usually didn't carry more than 30 cartridges for his musket, and even in the biggest battles rarely fired more than half. $\endgroup$
    – vsz
    Commented Jan 31, 2023 at 14:41
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    $\begingroup$ @Hobbamok Of course, firing in shifts was what they did with muskets anyhow. You'd have 1 group firing while the other(s) were reloading, or possibly one shooter with half a dozen muskets, and have support people behind him reloading the ones he wasn't currently firing. Girardonis would simply reduce the number of shifts/spare rifles needed. $\endgroup$ Commented Jan 31, 2023 at 14:46
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Steam or compressed air come immediately to mind.

It doesn't take long to figure out that a heated container with water inside will end up exploding. It might not be as handy as black powder, so it might not out-compete bows until other explosives are discovered or compressed air is made available.

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    $\begingroup$ @Graham, why? apply your reasoning to black powder and ancient guns.. did it only work for demolition? $\endgroup$
    – L.Dutch
    Commented Jan 29, 2023 at 11:20
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    $\begingroup$ You'd generate the steam in a specially reinforced boiler. This leads through a reinforced pipe to the back of the gun barrel. The pipe is stopped with a stopper which bursts at a certain pressure, which would take a bit of tinkering but not be impossible. You could even invent some sort of valve triggered by pressure. So the steam would build up pressure then burst out all at once. It could be done. Maybe better for cannon than handguns. Of course the necessary strong steel wasn't available on Earth until after gunpowder, pressurised steam was a later thing. $\endgroup$
    – Greenaum
    Commented Jan 30, 2023 at 0:17
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    $\begingroup$ This has been done before. The British used Holman projectors during world war 2 as an alternative to cannon. They were used as defensive armament on merchant ships. $\endgroup$
    – JRE
    Commented Jan 30, 2023 at 9:23
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    $\begingroup$ @AustinHemmelgarn Hmm, that might work. It'd be an "interesting" project to design the rupture disc, and I'm dubious about it being very accessible in pre-industrial days. But yes, I agree it'd make it technically possible. Nice one. :) $\endgroup$
    – Graham
    Commented Jan 30, 2023 at 10:08
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    $\begingroup$ As others have suggested, airguns are a real thing. They lack the muzzle energy of regular firearms but are certainly capable of lethality if scaled right. An airgun which gets its pressure from steam rather than mechanical action is also possible. $\endgroup$
    – pjc50
    Commented Jan 30, 2023 at 10:31
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As Willk notes, it's apparently possible to make working gunpowder without sulfur, it's just hard to ignite.

However, if your civilization really has no access to gunpowder at all (maybe due to lack of usable sources of saltpeter?), they could just jump straight to what was historically the next step in gun propellants in our world: guncotton (nitrocellulose).

Making guncotton basically just requires some way to produce concentrated nitric acid — which of course might be a problem if your world is poor in nitrates such as saltpeter. But there are several different ways of producing nitric acid (the modern process starts with ammonia, but you can also make it literally from thin air) and it's at least conceivable that, without easily mineable saltpeter deposits, your civilization might stumble upon a practical way to make and concentrate nitric acid before figuring out gunpowder.

Of course you can make saltpeter from nitric acid, once you have it, by reacting it with some source of potassium. But once you have nitric acid, you might well discover guncotton before gunpowder.

In particular, once you have nitric acid and some brave chemists playing with it, the discovery of guncotton seems all but inevitable. To quote the Wikipedia article I linked above:

Around 1846 Christian Friedrich Schönbein, a German-Swiss chemist, discovered a more practical formulation. As he was working in the kitchen of his home in Basel, he spilled a mixture of nitric acid (HNO3) and sulfuric acid (H2SO4) on the kitchen table. He reached for the nearest cloth, a cotton apron, and wiped it up. He hung the apron on the stove door to dry, and as soon as it was dry, a flash occurred as the apron ignited. His preparation method was the first to be widely used. The method was to immerse one part of fine cotton in 15 parts of an equal blend of sulfuric acid and nitric acid. After two minutes, the cotton was removed and washed in cold water to set the esterification level and to remove all acid residue. The cotton was then slowly dried at a temperature below 40 °C (104 °F). Schönbein collaborated with the Frankfurt professor Rudolf Christian Böttger, who had discovered the process independently in the same year.

By coincidence, a third chemist, the Brunswick professor F. J. Otto had also produced guncotton in 1846 and was the first to publish the process, much to the disappointment of Schönbein and Böttger.

Note the independent (and at least partly accidental) discovery by three chemists at almost the same time! This strongly implies that it was very much a case of it being "steam engine time", with the conditions simply being right for the discovery to be made by someone experimenting with the available chemicals, rather than the discovery itself being the chance result of some particularly uncommon luck or effort.

Of course, after guncotton was discovered, there was still a considerable amount of further innovation and refinement to be done to deal with issues such as storage stability and to produce improved types of "smokeless powder" such as ballistite (a combination of nitroglycerine, and guncotton) and cordite (nitroglycerine, guncotton, petroleum jelly and later nitroguanidine). But that's not fundamentally different from the gradual refinements and improvements made to gunpowder after its discovery too.

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    $\begingroup$ "....As he was working in the kitchen of his home in Basel, he spilled a mixture of nitric acid (HNO3) and sulfuric acid (H2SO4) on the kitchen table. He reached for the nearest cloth, a cotton apron, and wiped it up. He hung the apron on the stove door to dry, and as soon as it was dry, a flash occurred as the apron ignited. " I love thhe way they did chemistry in those days! $\endgroup$ Commented Jan 31, 2023 at 7:23
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It is possible that firearms aren't even used. Gunpowder has historically been fairly easy to produce and manufacture at scale, and while other responses such as coilguns, steam, and railguns are interesting to consider, they are often highly complex and fairly difficult to manufacture at scale, especially for an evolving economy or society. Coilguns and railguns in particular require rare earth materials that are unlikely to be found without advanced drilling and mining techniques, but historically mining was often done with - you guessed it - gunpowder.

In my opinion, it's likely that the primary source of weaponry in a sulfur-less environment would take the form of rockets - rocket propellants, such as ammonium/potassium compounds plus aluminum and oxides, are considerably more plentiful than REMs and their launch mechanisms involve fewer moving parts than many other forms of weaponry. Liquid propellants, such as nitric acid (TNT, which doesn't involve sulfur), and hydrogen peroxide, are also fairly inexpensive to produce relative to the amount of damage they can cause.

In my opinion the most likely scenario is a compressing of rockets into small explosive shells that can be fired from a device roughly the size of a rifle or a handgun. Such a device would probably be little better than an 18th-century musket, but consistent evolution in this field would likely enable the miniaturization of these devices and increased rate of fire and reload time.

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  • $\begingroup$ A boltgun then. $\endgroup$
    – Quinn
    Commented Jan 29, 2023 at 0:38
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    $\begingroup$ @Quinn I may be wrong but I always understood bolt guns to involve propulsion with compressed air or with springs, not with self-propelled bolts. $\endgroup$
    – dreamforge
    Commented Jan 29, 2023 at 1:00
  • $\begingroup$ Just checking, but you're not THAT Quinn? Youtube channel? An honour to meet you, if you are! $\endgroup$
    – Greenaum
    Commented Oct 7, 2023 at 17:47
  • $\begingroup$ Rocket propellants produce lots of hot gas, how is that different to gunpowder? Indeed firework rockets use gunpowder. Seems like if we're not allowed gunpowder, we're not allow equally, or more, effective chemical propellants. But if you DO want rocket-pistols, check out the 1960s Gyrojet which did just that! Now, the remaining "bullets" in existence cost a fortune, they're antiques, firing one is a rare experience! Some soldiers took them to Vietnam, as private property. $\endgroup$
    – Greenaum
    Commented Oct 7, 2023 at 17:49
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They might stick with bows and crossbows a lot longer

Black powder weapon advantages

There are basically two advantages to early gunpowder-based weapons, that both turned out to be quite useful in early modern Europe, and led to further development:

Siege weapons

Early modern Europe had mostly small armies, and lots of castles with tall but relatively thin walls that were easy to defend with small garrisons. These are almost uniquely vulnerable to early cannon. It took some time to develop cannon to the point where they could rapidly and reliably batter down those walls, but once that was achieved, walls suddenly turned out to be almost useless. (this didn't apply in china, as they mostly used much thicker walls, filled with earth)

This led to the development of fortifications with thicker, lower walls, but those couldn't rely on the difficulty of scaling them, so you instead needed a large garrison that could effectively threaten attackers. That leads us to the second advantage:

Guns are easy (relatively speaking)

That's not to say that a gun is trivial to make, to make ammunition for, or to operate, but it is much faster and easier to train a peasant to use a gun than it is to train him to use a (war)bow. So if you suddenly find yourself in a situation where you need to massively expand your army, and arm them with ranged weapons (spears are cheap and easy, but they won't help you much when defending a star fort), in order to defend your fortifications, they're the best option you have. This was very much the case in early modern Europe.

So what happens without black powder?

Later guns

Well, if the industrial revolution happens, as Ilmari Karonen says, eventually nitric acid will lead to the development of guncotton and other suitable explosives. That will almost inevitably lead to guns. Earlier, the development of pressure vessels might give you airguns, but until either of those are compelling enough to force a switch, armies might continue to use and further refine bows and crossbows.

State formation

Gunpowder-based warfare was very important to the political history of Europe. Without it, the nation-states that you know might not exist, which all sorts of knock-on effects.

The industrial revolution

For instance, the industrial revolution might not have happened there, or at all. In Britain, it required large coal deposits, the depletion of forests (for firewood and charcoal), the existing knowledge of early pressure vessels (from black powder weapons), all contained in a large state doing lots of trade (so greatly increasing production of, well, anything, wouldn't crater prices), allowing early "burn coal to power a very inefficient pump to drain the coal mine so you can dig up more coal" engines to be developed and adapted to power factories.

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Coilguns

Actually, it depends on how advanced these beings are. Assuming a level of advancement below or only barely that of modern humans, I would go for the compressed-air device suggested by L. Dutch above. However, as technology advances, there may be a better option. enter image description here

Meet the coilgun: this bad boy works by using magnetic forces to accelerate a projectile to supersonic speeds. Effective? Uh, did I say supersonic? This device is basically a handheld mass driver. Okay, so we don’t quite have these puppies yet, but hey, maybe your civilisation is farther ahead than us, tech-wise.

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  • $\begingroup$ Do you think these would be accessible during the eras where firearms were first introduced though? That has effects in terms of the world culture. $\endgroup$
    – Quinn
    Commented Jan 29, 2023 at 0:39
  • $\begingroup$ @Quinn most definitely not $\endgroup$ Commented Jan 29, 2023 at 18:52
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    $\begingroup$ “Okay, so we don't quite have these puppies yet” You, uh, might want to reword that section slightly… $\endgroup$ Commented Jan 29, 2023 at 20:03
  • $\begingroup$ @infinitezero Though it’s worth noting that that limitation is mostly a result of energy storage issues and simple knowledge. Coilguns use a lot of power, but pretty much everything else involved is actually very low tech, you just need decent copper refining, basic wire drawing, and a reliable source of relatively consistently sized ferromagnetic projectiles (both not especially difficult) and a basic knowledge of how ferromagnetic objects behave in proximity to coils of wire. $\endgroup$ Commented Jan 30, 2023 at 2:41
  • $\begingroup$ Pardon my asking but is this the Quinn with the ideas? Awesome Youtube videos, mate. $\endgroup$
    – Greenaum
    Commented Jan 31, 2023 at 11:42
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Mechanical Tension/Compression weapons

Prior to the advent of firearms, their nearest equivalent was probably the Crossbow and its bigger cousin, the Ballista.

Take a strip of bendy metal or wood, pull back the end via cords and possibly a winch.
Basically an adaptation of the slingshot for enhanced power and accuracy.
A well-made crossbow could put a metal bolt straight through the best body armour of the time at any range you could reasonably expect to hit at.
More than sufficient as a weapon of war, and substantially easier to train with than the Longbow it competed with. It made ranged combat something that could be done by minimally trained Militia and Helots rather than life-long professional bowmen.

You might also explore the Discworld concept of the Spring-Gonne. A spring-powered compact crossbow.
This concept may also be found in Frank Herbert's Dune in the form of the Maula Pistol. A spring-powered dart-gun loaded with poison darts.

Springs tend to pack a lot less force than a crossbow, in large part due to inefficiencies in the spring and challenges in manufacture, but they're excellent options with light projectiles.

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In the context of your setting, guns just wouldn't be used before the industrial age, where mass-producible alternatives to gun-powder would by readily available.

People would stick with alternatives, such as repeating crossbows ---the real-world chinese army used those until 17-hundred-and-then-some.

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If humans had no access to gunpowder, they would likely use alternative forms of propulsion for firearms, such as:

  1. Springs or compressed air
  2. Nitrogen-powered combustion
  3. Pneumatic or hydraulic pressure
  4. Electrical or magnetic systems
  5. Rocket propulsion

These alternatives would provide the necessary energy to propel a projectile out of the barrel of a firearm.

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Ye Old Elastic Materials

Since before the first gun, humans have used the principles of elasticity to fling sharpened sticks or small-to-medium stones at each other or at animals they wish to send back to their respective culture's creator.

Slingshots and Bows should suffice and don't use any chemical or electrical propellents, the ammo is even reusable, mostly.

Bows take more skill and strength to use, but you can train any old peasant to use a crossbow and children can learn how to fling a rick with a slingshot, plus the projectile is slow

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The Sims-Dudley Dynamite Gun was tested in the Spanish American War:

https://www.spanamwar.com/dynamite

With a different source of compressed air (it used a small black powder charge to throw shells) something like the Dynamite Gun might work for you.

If your world has lots of electricity to spare, consider calcium carbide:

https://en.wikipedia.org/wiki/Calcium_carbide

... which produces acetylene when wetted, delivering a pretty good bang:

https://en.wikipedia.org/wiki/Bamboo_cannon

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    $\begingroup$ In the preindustrial period there was no electricity $\endgroup$
    – L.Dutch
    Commented Jan 30, 2023 at 18:53
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There are plenty of air rifles available now, which, with a little tinkering, can produce pressures high enough to make them deadly to humans. They're only usually under-powered because of government regulation (speaking of the UK here). You could quite easily produce a deadly airgun. It's just a bit of plumbing and a bit of clockwork.

Before that, we used tension. Bows and arrows, and catapults. Crossbows were particularly deadly, armour-piercing even. To tension them ready for firing often took the strength of the soldier's whole body, putting their foot in a loop at the bottom and using a strong lever to pull the string back. The energy was stored in the springy steel.

EDIT: Browsing about steam-powered guns, https://en.wikipedia.org/wiki/Steam_cannon there were a few. Not great successes but if there'd been no gunpowder, perhaps they'd have put more work into developing them.

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Strong rubber bands (i.e. slingshots, or sling bows) could be a viable alternative, specifically if used in combination with some kind of device that allows tensioning them while investing less muscle power.

This guy might give you some ideas:
Joerg Sprave - @Slingshotchannel - YouTube

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    $\begingroup$ If they don't have rubber (and some ways of vulcanising rubber to make it strong instead of squashy latex, use a lot of sulphur), then the ancients used animal sinew, ie tendons, peeled into fibres and twisted into ropes. $\endgroup$
    – Greenaum
    Commented Jan 31, 2023 at 11:39

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