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I'm writing a story with a fantasy-adventure-like background. The usual world where adventurers take quests and explore dungeons, but instead, I want my main focus to be on the support roles. Those include alchemists, blacksmiths, librarians, etc.

The main character is Leo, an average alchemist who just opened a potion shop. His shop is right next to an average blacksmith, named Claire, who he is friends with. He was able to quickly grab customers by taking personalized requests for advanced potions. However, It got to a point where he needed to create potions in bulk by mixing a good quantity of ingredients in a cauldron.

Leo decided to ask Claire for one. Claire is very skilled in what she does, but she lacks quality equipment and materials. Both of them have been switching favors between each other, and she feels like she owes him. With that in consideration, she will do her best for his request.

My question is, how hard would it be to produce a large, good quality cauldron for alchemy?

The best answer should:

  • Suggest a good material for a cauldron that consistently keeps an uniform temperature when over a heat source. Bonus points for resilience and cleanability.
  • Estimate the amount of time needed for Leo’s request.
  • Explain in some detail how Claire would create this cauldron. I have some knowledge in mathematics, physics, biology and technology, but the only thing I know about blacksmithing is that temperature is important.

Edit: Claire has easy access to copper, iron, lead and tin, but she should be fine with spending a little more on rare/precious metals like silver/gold. Other metals like Chromium, Zinc, and platinum were discovered recently, meaning that smiths in general are not sure about their properties (but she might take this opportunity to test one or two). She is able to make alloys out of the previous mentioned materials. She is also not limited to metals.

Claire usually uses coal, meaning that the highest temperature she can reach would be around 1900ºC. Heating speed may be to your liking.

The technology she has available is similar to one we had at the end of the 17th century.

Leo also explained to Claire that the measurements and ingredients used in the potion making process should be as precise as possible. If not, the potion’s effect is either downgraded, or worse, it can trigger secondary undesirable effects. This means that Claire might need to have special considerations because of any possible corrosion. He also warned that the cauldron might reach 200 ºC for long periods of time, not understanding if that makes any difference.

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    $\begingroup$ Cooking pots were commonly created in medieval times and earlier. Any large iron pot could be used for alchemy. What is the critical difference between a large cooking pot and a cauldron for alchemy? $\endgroup$
    – David R
    Jun 4, 2021 at 23:21
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    $\begingroup$ @DavidR Nothing is noted in the question about the medieval period, whereas alchemy comes from a 4000 year-old tradition. I agree that the question needs details and clarity though. $\endgroup$
    – Escaped dental patient.
    Jun 4, 2021 at 23:45
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    $\begingroup$ Early metal works hammered metals into pots/cauldrons/bells before casting became reliable. What is the "tech" setting you are dealing with? 1500s Europe, Bronze Age Mesopotamia, Something else? Without knowing more details it is hard to advise if Claire would lean towards hammering or casting. Also, does it have to be metal or could she use clay or glass as a viable cauldron material? $\endgroup$
    – JonSG
    Jun 5, 2021 at 0:06
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    $\begingroup$ Not really an answer per se but it's worth noting the comment at reddit.com/r/Blacksmith/comments/4wjmzb/… saying "As for the technique, the vast majority of medieval cauldrons were riveted together, not unlike the spangehelm type of helmet. "Single piece" cauldrons rised from a circular sheet of metal weren't really practical to make until High Medieval period. The cauldrons were usually made of rivetted pieces." The link has more text as well as a link to a photo of a cooking cauldron found at Oseberg. $\endgroup$
    – GrumpyYoungMan
    Jun 5, 2021 at 1:23
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    $\begingroup$ As alchemist, I'm telling u - do not use reactor vessel as your measuring device, measure components first, separatly with volume mass measuring devices, then dump in reactor vessel. Doing otherwise is eyeballing things at best.(not exactly, as there are reactions when u add stuff until certain processes going, and then u do not need measure a thing) $\endgroup$
    – MolbOrg
    Jun 5, 2021 at 11:29

8 Answers 8

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The easy, adequate way: Copper
As per Xavon_Wrentaile's answer, a simple copper of bronze (not brass!) cast cauldron will work just fine. The copper will help distribute heat. The material is strong and durable. It resists chemical, acid and alkaline attacks reasonably well, although it will tend to lose a bit of copper into any acid solution in it.
Most importantly, it uses materials and techniques that are easily available to a blacksmith.

not so easy, also not so adequate: Cast iron
Exactly as per the copper cauldron, using a sand casting.
The problem is that cast iron is quite brittle, very much more subject to contamination and etching by adicid contents than copper is, and worst of all: cast iron is porous. It absorbs stuff, potentially contaminating future project with residue embedded int he cauldron itself.
On the positive side, the making of a cast iron cauldron should still be within the capabilities of a blacksmith, although much harder than making one from copper.

The easier, but not so adequate way: Pewter
Cast your cauldron from Pewter.
This is easier even than making a copper cauldron. The materials are very easily sourced and handled.
Unfortunately, its temperature resistance is not so great, and there is the small problem of it leaking lead into both acid and alkaline solutions within it. Lead poisoning is significantly worse than copper poisoning! There is also the tiny problem that the specified 200C heat tolerance requirement is very close to the actual melting point of the metal! Melted cauldrons would be a real danger.

The ideal: but impractical to make: Glass.
A good thick, strong glass cauldron, with no impurities, defects, bubbles etc.
A good glass cauldron would withstand great heat, would not contaminate the contents, and would tolerate even the most virulent chemical concoctions that an alchemist could dream of.
Glass does not conduct heat that well, so the user will need to be very patient, to prevent hotspots.
The problem here is that making good glass, or even making any glass, is well beyond the skill and tool capabilities of a blacksmith.

Even better, but impossible: Modern Steel
The ideal material is of course a nice corrosion-resistant stainless steel. Good old modern cookware!
Unfortunately, the making of suitable iron/chrome/nickel/carbon alloys is well out of the capabilities of a blacksmith.

. . .

Has your Alchemist considered not using the Blacksmith, but rather getting a nice line of disposable pottery cauldrons from the Potter?
A glazed pottery cauldron should have similar inertness as the glass cauldron.
Sure they will wear out much more quickly, but the cost should be immensely lower, and it allows for the idea of one-brew disposable cauldrons. Possibly even brew-in-storage-container alchemy? Guaranteed fresh, never removed from its cauldron, untouched by human hands. Fresh to you, the consumer as pure as the day it was made.

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    $\begingroup$ It's worth pointing out that only cast iron and steel would be made by blacksmiths. Copper's made by redsmiths, pewter's made by whitesmiths, and glass is made by glassblowers, who aren't even smiths at all. $\endgroup$
    – nick012000
    Jun 5, 2021 at 17:11
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    $\begingroup$ @nick012000 quite true. however , the OP specifically wants the Alchemist's blacksmith friend to do the job. Strictly speaking, blacksmiths never work with molten metal, thus no castings! But, a blacksmith should be able to kludge totgether a viable copper melt-and-pour casting. $\endgroup$
    – PcMan
    Jun 5, 2021 at 17:32
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    $\begingroup$ @nick smiths often worked with more than one metal, you are only describing their specialty. It was quite common for a blacksmith to also work in copper or bronze. $\endgroup$
    – John
    Jun 6, 2021 at 2:58
  • $\begingroup$ Is it practical to hybridise, by glazing the interior of a copper cauldron or copper-coating a ceramic one? $\endgroup$
    – Anon
    Jun 8, 2021 at 5:59
  • $\begingroup$ Glazing the interior: see Enamelware. $\endgroup$
    – PcMan
    Jun 8, 2021 at 11:48
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Easily and quickly

Given the very unrestrictive requirements, all Claire needs is some clay, two iron rods, enough copper or bronze for the cauldron, and a forge that can get hot enough to melt the metal.

Make a clay mold of the cauldron. Use the iron rods to suspend the inner mold in the outer mold. Melt the copper/bronze and pour into the mold. Cool. Chip out the clay. Remove the iron rods (use the holes to attach handles). Polish. Deliver.

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    $\begingroup$ The cauldron should be good and thick, because while that will make it slow to heat it up, it will hold the heat beter. $\endgroup$
    – Mary
    Jun 5, 2021 at 1:03
  • $\begingroup$ A copper cauldron would be great for cooking (especially for beating eggs and whipping egg-based creams). I doubt, though, that it will work well for alchemy since it will be exposed to highly reactive materials. I am no chemist, so someone needs to verify this point. $\endgroup$
    – Otkin
    Jun 5, 2021 at 4:46
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    $\begingroup$ @Otkin copper is quite exceptionally good at resisting corrosion. It is vulnerable to some acids, but then absolutely everything is, to some extent. Even a pure glass cauldron would be, and making a good temperature-tolerant, large, glass cauldron would be impossible n the environment specified. $\endgroup$
    – PcMan
    Jun 5, 2021 at 8:46
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    $\begingroup$ Blacksmiths work in iron and steel. Copper or bronze items are made by redsmiths. $\endgroup$
    – nick012000
    Jun 5, 2021 at 17:09
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    $\begingroup$ @Otkin ceramic is far less reactive. $\endgroup$
    – John
    Jun 5, 2021 at 19:35
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Claire might have access to materials other than iron and steel, but she wouldn't be legally allowed to work with them.

Medieval cities organized skilled trades using the guild system, which was granted a legal monopoly within the city limits on the performance of their trade and the ability to set prices for the items that they produced. In particular, "blacksmith" refers to the smiths which worked with iron and steel; smiths who worked with other metals formed their own trades and own guilds (whitesmiths worked tin and pewter, redsmiths worked copper, bronze and brass, and goldsmiths and silversmiths often shared a guild), and Claire wouldn't be legally allowed to work with those materials - this could be considered analogous to how an electrician wouldn't be allowed to work on air conditioning units today, unless they were also certified as an air conditioning tradesman.

If Claire is a journeyman or master blacksmith (and she would be, if she's running her own store and working independently), she would be well aware of this, and would operate within the constraints of her guild's regulations. If she's making Leo a pot, it would be made from iron or steel, because those are the materials she would be legally allowed to work with. If she wanted to work with other materials, she'd need to gain the approval of the other guilds of smiths first.

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    $\begingroup$ I agree. The question /specifically/ said that Claire was a blacksmith, and as such even if she has access to other materials she might- even if she doesn't realise this- be completely unable to achieve the desired result using anything but wrought (/not/ cast, she isn't an iron founder) iron... and if she tries, the result might fail unpredictably and amusingly :-) $\endgroup$
    – Mark Morgan Lloyd
    Jun 5, 2021 at 17:41
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    $\begingroup$ Someone wanting to openly work with other materials would need the approval of the appropriate guilds. There might be story reasons, however, for doing things on the sly, in which case the question of what's legal would be less important than what one could get away with. Perhaps the alchemist might also need the assistance of someone with an excuse to acquire some heavy copper artifacts and have them "disappear". $\endgroup$
    – supercat
    Jun 5, 2021 at 19:50
  • $\begingroup$ This depends on where in the world you were. I am quite sure there were no such guilds among the norse, the chinese, the japanese, and in the arab world in general. $\endgroup$
    – The Square-Cube Law
    Jun 6, 2021 at 2:13
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    $\begingroup$ "To work in other materials, get the approval of other guilds or smiths first" actually works out to Claire trades jobs. The coppersmith makes the copper cauldron and Claire makes them some horseshoes or door hinges or something. $\endgroup$
    – Harper - Reinstate Monica
    Jun 6, 2021 at 21:22
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    $\begingroup$ @TheSquare-CubeLaw ‘The first Norwegian guilds are mentioned in a royal regulation for Bergen og 1293/1294. Dere is mentioned a goldsmith guild, a blacksmith guild, an ale-brewer’s guild and a journeyman’s guild. We otherwise know little of these guilds.’ (‘De første norske laugene er nevnt i en kongelig forordning for Bergen fra 1293/1294. Her nevnes det et gullsmedlaug, et jernsmedlaug, et ølbryggerlaug og et svennelaug. Det er lite vi ellers vet om disse laugene.’) Store norske leksikon: ‘laug’. Yes, the Norse had guilds. $\endgroup$
    – Canned Man
    Aug 28, 2022 at 0:36
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Although PCMan's answer covers most options in-depth, I believe he is missing the best solution which is tin lined cast iron or copper because it avoid the reactivity problems of iron/copper with acids. It does have a somewhat low melting point of ~450 degrees f (~230 c) but the inside of a cauldron shouldn't get that hot if there is anything in the cauldron (that's why tin lined skillets can be used on high heat well over >450 degrees).

It would have been available in the Middle Ages (and before) and is still used today on copper pans. Yes, maybe strictly speaking a Tinsmith or maybe even the Tin Man would be the maker, not a blacksmith, but I doubt the question asker is concerned with that and the process is simple enough.

Claire would cast the iron in a clay or sand mold as PcMan said, or hammer out the copper into its final shape. Then the cauldron is heated and some tin melted inside and brushed/wiped around until a thin coat is applied. The excess is wiped/poured out. Might the repeat process to even out. Should be able to find youtube videos of this process.

The tin had to be periodically re-applied, probably on the scale of years unless Leo carelessly scratches it with a metal ustensil! Which could add opportunities to your story.

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    $\begingroup$ Please note that the 450 degree melting point is in Fahrenheit. In Celsius (which the temperatures of the question are in), it's 231 degrees. $\endgroup$
    – AI0867
    Jun 7, 2021 at 11:28
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She may already have some cauldrons to sell

cauldrons were a common thing for smiths to produce. Cooking in a pot was the norm for medieval and renaissance cooking. At the time bronze or copper cauldrons were more common but plenty of iron ones also exist. both could be made either by casting or riveting and/or soldering. Riveting is how the largest ones were made but cast ones tended to be thicker and this heated more evenly, so method depends on what you mean by "big". A real apothecary (potion maker) is not make huge volumes in a single pot, they would just have more pots to make more things at once. A large pot also means you will not have a consistent temperature, because you are cooking on a wood fire, which is not a precision heating method.

hammered or riveted copper pots were also becoming common at the time, but it is unlikely a blacksmith will know how to do that, although she may very well be able to trade with the local coppersmith, there would be a lot of cross trade. coppersmiths would have and need a lot of blacksmith made tools so a trade would likely be easy, making such a pot would take a few days.

Reactivity is not really an issue for an apothecary, they are not making anything terribly corrosive. If you need to make powerful acids you do it in clay pots. your apothecary may even already have a cast metal mortar.

Making a cauldron should be something she has done often. Metal cauldron were very common in the medieval and renaissance period, this is the era of cast cannons after all. it was considered a step up from fragile clay pots that were also common. It should take a few days for a riveted one or less than a day for a cast one. You can find plenty of video on the internet of each being made, there area lot of people reenacting these techniques.

Riveting is literally making the pot in sections and riveting them together and possibly soldered. Riveted pots often have to be sealed with lead after they are made to prevent leaks (sealing with tin is more common but will not take 200*C.

Casting would involve a clay or greensand mold that molten metal would be poured into. here is a great video of casting a cooking pot, the process would be very similar.

She may also have a broken one that can be fixed, many cauldrons show signs of repair (mending), usually patching a crack. Some visuals to see what you are working with.

Recreation of a riveted iron cooking pot

![enter image description here

medieval cast iron cauldron

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Medieval cast bronze cauldron

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Medieval riveted bronze cauldron

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Metal cauldrons were quite common. Example of a Medieval field kitchen from Il Cuoco Segreto Di Papa Pio V (The Private Chef of Pope Pius V), by Bartolomeo Scappi, Venice, 1570.

enter image description here

Plate showing 17th century coppersmiths making cauldrons of various sizes.

enter image description here

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    $\begingroup$ I think your underestimating the time to do casting by a order of magnitude. I mean IF you have a setup for casting then yes. But casting is, well... hard. IT looks exceptionally easy when you have the right equipment and patterns. Even when i have access to a modern casting facility, steel is way out our league except maybe one time a year. But the average smith would have to contend with riveting the cauldron of any size except maybe a tiny one. Mainly because the energy needed to melt any sizeable amount of metal is well beyond the energy requirements of most medieval operations. $\endgroup$
    – joojaa
    Jun 6, 2021 at 11:16
  • $\begingroup$ And filling big casts uniformly requires some expertise. It is unlikely that castings were done by your average smith. After all just the anvil itself would account for half of the lifetime earnings of a smith. $\endgroup$
    – joojaa
    Jun 6, 2021 at 11:18
  • $\begingroup$ @joojaa Its not actually that hard, many blacksmithing products are cast, and as I said making pots and cauldrons would be a normal thing for a smith at the time and many were cast. I have made castings it does not take long to make. If the smith is in a city they likely have access to a larger furnace, they may not own it but they certainly have access to it. and a cauldron does not use that much metal and unlike bells do not require that much skill. $\endgroup$
    – John
    Jun 6, 2021 at 12:55
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    $\begingroup$ A big pot is hard to cast because you need to make a big pattern, you need lots of headspace and your result can not be porous. Its not as hard as casting a bell but the bigger the cauldron the harder its to cast. Making a big pattern takes atleast a day plus a day for preparation, also you need a big crubicle and a team of 3 people for bigger casts. Its just that i feel its unlikely your random blacksmith would have equipment for casting. There were specialists for things like bells and cannons. But then what do i know ive only ever sandcast tank threads and colibris with investment casting. $\endgroup$
    – joojaa
    Jun 6, 2021 at 13:52
  • $\begingroup$ @joojaa both things that are more complex with a lot less slop than making a cauldron, investment in particular is far more involved, this is a much simpler much rougher method. And that is assuming she does not already have forms for making cauldron molds, As I said they were very common at the time, often made in multiple pours. this is not like lost wax casting, this is sand casting. its is a very simple technique. $\endgroup$
    – John
    Jun 6, 2021 at 15:07
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The Gold Standard:

The two most important metals in alchemy are gold and mercury (and I'm hoping you aren't adding mercury to your potions). If inert is critical, then plate the inside of your cauldron with gold. Even a cooking pot lined with gold will be a cauldron. Its chemically inert properties were deeply important to alchemy, and Aqua Regia was needed to dissolve gold. The whole quest for the philosopher's stone was about making gold from base metals. The melting point is higher than people think (1064 C) but it is fragile, so it would need maintenance. Use a gentle mixing tool to cut down on wear. But chemically, the stuff is extremely inert and will be useable over and over. It would heat well due to its extremely high thermal conductivity. Plates of gold are extremely easy to work with and the whole task could be done very quickly.

If cost is not an object, then make the whole thing from gold! Casting gold is relatively easy, and could be done with sand and wax (or simple clay) as is often done today with the production of bells. A wax cauldron is made, packed with sand, fired to melt out the wax (the sand hardens) gold poured in, then the sand is simply chipped away. Otherwise, gold is amazingly malleable and the whole thing could be pounded out.

The whole thing can be supported on the outside with other materials to give it greater structural support if needed.

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    $\begingroup$ @nick012000 The OP explicitly put gold on the available list in the question, and a metal worker would find it easier to make things out of gold than iron. Gold is easier, but often the things people make from gold require a higher skill level with fine crafting. $\endgroup$
    – DWKraus
    Jun 5, 2021 at 17:12
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    $\begingroup$ Goldsmithing requires entirely different techniques to blacksmithing, and was regulated into different guilds. A blacksmith wouldn't be legally allowed to work with gold, since that would violate the monopoly of the goldsmiths' guild on that trade. $\endgroup$
    – nick012000
    Jun 5, 2021 at 17:14
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    $\begingroup$ @nick012000 Then the whole premise of the question is no good, since it is asking what metals the smith should make the cauldron out of, and you're saying a blacksmith by definition is only capable of working with iron. This is for a fantasy-adventure setting. I think you're getting a little hung up on the details of the middle ages and our reality. I didn't criticize your frame-shift answer (it's a fair critique), but it doesn't really meet the OP's needs. And I think the biggest barrier to gold is the cost of making a large object out of GOLD, although gold is cheap in fantasy worlds. $\endgroup$
    – DWKraus
    Jun 5, 2021 at 17:39
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    $\begingroup$ Gold is good vs many chemicals, but mercury will amalgamate with it (and silver) and turn your nice gold-lined pot into a mercury amalgam-lined pot. $\endgroup$
    – docwebhead
    Jun 6, 2021 at 13:25
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    $\begingroup$ @docwebhead Part of the reason I stated that I hoped they weren't adding mercury to their potions in the opening line, although mercury was very important to alchemists. But if Chinese emperors can consume mercury in an attempt to become immortal, who knows? It's fantasy. $\endgroup$
    – DWKraus
    Jun 6, 2021 at 13:38
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There are several options which come to mind.

Probably the simplest is go down to the potter and buy or commission a clay pot. Or Clare could try making one her self*.

A more obvious answer is just get her to beat out a caldron from either copper or iron/steel.

I have made small copper bowls with just a concave surface cut into the end of a piece of wood and a peening hammer. It just takes a lot of carful taps and you can stretch the copper in to shape. You can soften the copper (which work hardens) by heating it and then quenching it in water (Which is the opposite to steel FYI), as you go.

Here is a very crude version: https://www.youtube.com/watch?v=7e6Z9QQieAk

And here a craftsperson making more complex copper tea pots etc: https://www.youtube.com/watch?v=odWl4M-Pzw0

Being a blacksmith Clare could quite easily do something in-between the two.

The same thing can be done with an iron/steel. It just requires more heating and beating. But that is something Clare already has the skills and equipment for.

*FYI here is examples of the simple tools etc which are required to make suitable sized and shaped pottery pot/caldron https://youtu.be/52HKSwkI1hs

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Alchemical Glazing

Gold is fairly unreactive, so are glass and ceramics. Even copper/iron can last a while. But why limit it to mundane materials?

Your alchemist can take an ordinary cauldron, and buy a small batch of expensive ingredients from adventurers to make a magically inert (and reasonably tough) coating on the inside. Claire's role in this can be as involved as you wish, and use any of the above manufacturing techniques.

Of course, this glaze may require regular reheating, or corrode the copper on the outside. Or the tools used to make the glaze may be sacrificed, so the smith has to make/repair them.

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