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In this scenario a kingdom that has not yet invented black powder has been invaded by an enemy that possess cannons and matchlocks. Since the invaders are few in number the defenders managed to beat them back and steal a large cache of powder. They are extremely concerned that the invaders will return in force and wipe them out. Therefore they want to learn how to make their own black powder and manufacture it before the enemy returns (which they think could be a few years.) Here are some caveats:

  • The defenders took no prisoners successfully, so they can’t learn the recipe through coercion or bribery.
  • The defenders have no written recipe or manual from the invaders.
  • The defenders have a tradition of intellectual curiosity and a pseudo alchemy/primitive chemistry but have not independently stumbled on gunpowder. They are however aware of all three components of gunpowder (but have no idea that those things together flash.)

So is it possible to reverse engineer black powder, and if so what method would be most efficient?

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    $\begingroup$ Whatever procedure you discover from answers must be contrived in your story. Consider Roman Concrete. It took 2,000 years to figure out the chemistry and another six to maybe figure out the recipie. And that using modern tech. So, your in-story solution will be contrived. IRL reverse engineering chemistry is very difficult. $\endgroup$
    – JBH
    Oct 26, 2022 at 15:49
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    $\begingroup$ Roman Concrete was mostly just difficult to figure out because its so counter intuitive. The only significant difference between it and other concreates we've been using for hundreds of years was the use of seawater instead of freshwater. Salt is known to damage concrete made with freshwater; so, adding it intentionally to your mixture is not the kind of thing modern engineers had any good reason to experiment with. $\endgroup$
    – Nosajimiki
    Oct 26, 2022 at 17:02
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    $\begingroup$ @JBH: (1) It is not 2000 years, more like 1400 -- last Roman concrete construction was in the 3rd century, and by the 17th I know for sure that concrete was a well-known construction material. (2) Which is perfectly understandable given that chemistry only emerged as a science in the 1700s. (3) The chemistry of Portland cement was figured out within 50 years of figuring out what this chemistry thing was in the first place. (4) They had and used concrete in the 17th century at least, which I know because it was used in the building of the Canal du Midi around 1670. $\endgroup$
    – AlexP
    Oct 26, 2022 at 17:02
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    $\begingroup$ @AlexP That's all interesting.... what's your point? The provided answers so far are cool, but none of them would be an intuitive process to the "scientists" of the OP's time period. Did the Europeans discover gunpowder independently, reverse engineer it, or obtain the formula from the far east? If I recall my history there's a debate between independent discovery and acquisition of the formula - nobody believes they reverse-engineered the formula. $\endgroup$
    – JBH
    Oct 26, 2022 at 17:08
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    $\begingroup$ @JBH: AFAIK the Europeans discovered gunpowder independently, at least functionally. Maybe the original European source got the original formula from somewhere else, but that doesn't matter. For all practical purposes, the development of gunpowder in Europe is independent of any other culture, and went along very different lines: by the early 14th century Europeans (and neighbours, such as the Turks) had effective, operable cannon, and nobody else did. The rest is history. $\endgroup$
    – AlexP
    Oct 26, 2022 at 17:23

5 Answers 5

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Much of chemical analysis in the age of alchemy was done by taste and smell. Yes, this was very hazardous.

First thing is that anyone with a good sample will notice the sulfurous smell of gunpowder. The black color (and the way it leaves black dust when it's handled) would suggest charcoal is involved.

As @L.Dutch suggested, the taste of potassium nitrate is quite distinctive (to an alchemist, anyway) -- sal petre or "rock salt" was well known in Europe before the secrets of making gunpowder found their way from China to the west; it was used to make nitric acid.

Once those three ingredients are known, it would be a matter of testing known to alchemists (in our timeline) before 1300 CE to get a pretty close idea of the proportions.

Then comes the hard part. If you just mix the ingredients, even in perfect proportion, the product will just burn (sorry, Captain Kirk, if the diamonds didn't nix your bamboo cannon, the burn rate would). Instead, one must grind the saltpeter and sulfur into the pore in the charcoal, a process usually done with the "green powder" kept damp -- both to reduce the risk of ignition from friction, and as an aid to getting the saltpeter inside the charcoal. This makes what was called "serpentine" powder (probably because one of the early guns was a serpentine, referring to the shape of the holder for the glowing match). Once everything has been ground to the point where the ingredients can't be separated, then one must press the powder -- again, done damp, this makes a hard cake which, when thoroughly dried, is broken up and sieved to size the granules. This is "corning" and produces powder that would serve well through the 19th century -- essentially similar to what's still sold today (except modern powder gets one additional step, tumbling with graphite to coat the granules, making them meter more smoothly and offering slight protection against accidental ignition by static sparks).

In our history, it took more than two centuries for powder (at least in the West) to progress from "fireworks" to gun propellant, and that was after Westerners in the late 13th century had learned from traders what the Chinese put in their powder (which, by then, the Chinese were using in war rockets and small bombs, perhaps even primitive guns).

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    $\begingroup$ That's "corned" gunpowder. It is of course much better than "serpentine" gunpowder made by grinding the components together dry, but it was a later development. By the time that corned gunpowder was developed, everybody who was not an illiterate barbarian already knew what gunpowder was. The question is set in the fleeting time period when some people knew about gunpowder and some didn't. $\endgroup$
    – AlexP
    Oct 26, 2022 at 17:32
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    $\begingroup$ @AlexP Or, as I read it, when the less advanced folk know about it, from it being used against them, but lack the knowledge to make it. BTW, thanks for the reminder about "serpentine" vs. "corned" -- I've thought about making my own, and remember the process to get essentially modern powder, and forgot it was used for a century or more without corning. $\endgroup$
    – Zeiss Ikon
    Oct 26, 2022 at 17:41
  • $\begingroup$ I wonder whether that grinding process could be reverse engineered too. I don't know if this is true but you might be able to see by looking at the powder that it doesn't contain any separate grains of saltpeter or sulphur, and therefore conclude that the ingredients must be more thoroughly combined somehow. (This would be easier if you have some kind of magnifying glass, which I guess you might or might not do given the historical period.) $\endgroup$
    – N. Virgo
    Oct 27, 2022 at 6:29
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    $\begingroup$ @N.Virgo Magnifiers were known in Roman times, but clear optical glass was very hard to come by (I've read that one of the Ceasars had an emerald cut/ground to a concave lens to correct nearsightedness). $\endgroup$
    – Zeiss Ikon
    Oct 27, 2022 at 10:59
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    $\begingroup$ You might want to check out the (re)invention of gunpowder in Hoban's Riddley Walker: en.wikipedia.org/wiki/Riddley_Walker $\endgroup$ Oct 27, 2022 at 20:52
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Burning it will produce an obvious odor of sulfur dioxide, showing it likely contains sulfur. Tasting it will show it contains some types of salts, likely immediately identifying saltpetre as at least a major component. This probably won't be a surprise, the substance was known from ancient times.

First, wash in pure water. Filter the solution and crystallize the soluble components. Taste, color, shape of the crystals, their solubility, their weight, their behavior when put in a flame...it'll be pretty straightforward to verify what you have as high-purity potassium nitrate, or saltpetre.

Then, the presence of some sulfur in the remainder will be easily identifiable by smell, and the appearance strongly hints of charcoal. Sulfur can easily be distilled off and recrystallized from vapor.

This leaves a black powder strongly resembling charcoal. With further heating, it burns without any odor (except maybe some weak sulfur residue), like charcoal would. Maybe it's charcoal?

You now have three probable components and their rough proportions. You can now mix them, and...find that the result doesn't work nearly as well as the black powder you analyzed. You can now waste a lot of time trying to identify the nonexistent missing ingredient (maybe it's coal, or some specific kind of charcoal, or treated somehow?), or work out that what you're missing is the manufacturing process that intimately incorporates the sulfur and saltpetre into the pores of the charcoal. A close examination of the original and noting that it's not just three separate powders mixed together, and is probably a lot coarser than the extracted charcoal, might put you on the right path. A microscope would help, if you have such a thing.

How long this is likely to take depends on how sophisticated the original blackpowder was and how sophisticated you need the reproduction to be. The actual history of black powder development spanned centuries and involved many different approaches of varying effectiveness, and quite a few fires and explosions.

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They don't need to reverse engineer gunpowder at all

The concept of a gun is a far more important thing to discover than any particular propellant. Gun powder is just one way of firing a bullet using expanding gasses, but you don't need gunpowder. What you need is a rapidly expanding gas. To this end, what you are looking for is anything that burns, and a method for making it burn very quickly and any alchemist from any time period probably has access to at least one substance that meets that requirement.

To prove this point, when I was little, my 12 year old brother figured out how to make a gun that could fire a steel ball without gun powder. He read a book about how medieval cannons worked, and then within a few days of using what resources he had at his disposal, he designed his own powderless gun.

In his case, he solved the problem with alcohol. While alcohol does not explode like gunpowder, he's already observed that it creates a fireball when you first light it from the vapors in the air; so, he fashioned a simple hand pump attached to a screen to aggravate the alcohol inside a sealed tube to fill the tube with as much vapor as possible, then ignite it. Basically he got around the need for a rapidly self-oxidizing reaction by using a thermobaric explosion as the propellant. The result was a small gun that could crack plywood using a 1/2" metal ball. With a bit more refinement, the technique could be scaled up to a weapon of significant military value (at least compared to other early firearms).

And this is just one alternate solution. Maybe your alchemists can't figure out any explosives; so, your blacksmiths figure out how to make a compressed air gun instead. Or maybe they use honey or coco powder instead of charcoal which have both been used in certain historical gunpowder recipes. Maybe they come up with a working design for a steam cannon. Heck maybe their knowledge of chemistry is good enough they can skip straight to figuring one of the variations of cordite having just not had a good reason to want to make something like that yet.

My point being that if a 12 year old boy can figure out how to make a gun within days of learning how they work, then somewhere in your kingdom is an inventor who can look at a guns mechanical features and figure out how to make some sort of analog with or without an exact black powder recipe.

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    $\begingroup$ I like it. This comes up in time travel stories a lot too. Or alien visitation stories. If every top scientist in the world got a good look at a clearly levitating UFO emitting no noise, then simply knowing that such a thing is scientifically feasible will set off a wide range of experimentation to figure out "how". Financing "anti-gravity device research" is probably hard to come by today (because it's not "how", it's "if") but if it was shown to absolutely be possible it would spur major research immediately. $\endgroup$
    – JamieB
    Oct 26, 2022 at 20:52
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    $\begingroup$ Great answer. Farmers deal with this today (grain dust explosions). Under the right conditions, there are a lot of things that can create a satisfactory boom. $\endgroup$
    – JBH
    Oct 26, 2022 at 22:03
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    $\begingroup$ The problem is that most "things that go boom" aren't suitable for guns. You need a low explosive, one where the reaction moves slower than the speed of sound in the explosive. Most explosives are high explosives, where the reaction moves faster than the speed of sound, generating a shockwave that is highly effective at shattering gun barrels. $\endgroup$
    – Mark
    Oct 26, 2022 at 22:33
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    $\begingroup$ The limitation here is that gunpowder (as well as other explosives) contains oxidizer in its mix. Alcohol (and most other things that burn) does not. Creating an explosive mix (ex. alcohol + air) is either an accident or an engineering challenge of a level that exceeds the level of gunpowder making. It's relatively easy to create a "proof of concept", but very challenging to create a cannon which has practical value. $\endgroup$
    – Alexander
    Oct 27, 2022 at 1:03
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    $\begingroup$ @JamieB: Examples at scifi.stackexchange.com/questions/74093/… and scifi.stackexchange.com/questions/74090/… for stories involving trying to leverage that trope. $\endgroup$ Oct 27, 2022 at 13:11
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Black powder is made by mixing potassium nitrate, charcoal and sulfur.

First step would be to try treating the powder with water: charcoal and sulfur would not be dissolved, potassium nitrate would. The solution water could then be tested to assess the nature of the salt. A possible testing would be by taste, as it is odorless with a sharp, cool, salty taste.

To separate coal from sulfur, sour gas could be used, as sulfur it is well soluble in it. Sour gas is natural gas or any other gas containing significant amounts of hydrogen sulfide. Alternatively, other organic solvents might be employed.

Once the ingredients are known, it would be a matter of experimenting with the relative ratios until finding the right one.

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    $\begingroup$ It may be useful to explain that black power is a mixture, not a chemical compound. In the early days it was a coarse mixture. The components can easily be identified under a modest magnifying glass -- at least the yellow sulfur and black coal are unmistakable. Blowing gently over the powder will tend to separate the components. $\endgroup$
    – AlexP
    Oct 26, 2022 at 11:26
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    $\begingroup$ I wonder if the potassium nitrate would crystallize when you let the dissolved gunpowder dry out. $\endgroup$
    – Willk
    Oct 26, 2022 at 13:20
  • $\begingroup$ @AlexP I know gunpowder is a mixture, I’m just asking how someone who’s never been taught about it would figure out it’s components. $\endgroup$
    – user71781
    Oct 26, 2022 at 16:20
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    $\begingroup$ @NixonCranium: You look at it closely, maybe with a magnifying glass. You notice that it is made up of something black which looks suspiciously like coal dust, something yellow which looks suspiciously like sulphur, and some mysterious white dust. You separate the components, maybe by dissolving the white dust in water (the coal and suphur don't dissolve) and crystallizing it by evaporation. You taste the white crystals, and identify saltpeter. (Remember that all three components were very well known ever since the Antiquity. The new piece of knowledge is what they do when ground and mixed.) $\endgroup$
    – AlexP
    Oct 26, 2022 at 16:45
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Have a skilled alchemist look over it with a magnifying glass and taste it.

It's a mixture of a few common substances, not some fancy chemical compound. Just have a professional look at it. They should be able to see the distinctive components and get extra information by smelling and tasting them. Sulfur is very distinctive in appearance and taste and smell, so is coal, potassium nitrate is a bit harder since it's a white powder, but the salty sharp taste can be distinguished with experience.

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