Some smelting data

[Krougal]

So I got tired of guessing how much time & fuel for smelting and alloying and started crunching some numbers (or rather making Gemini do it, which might have been more work than doing it myself)

The formula I came up with from the wiki would be  (I apologize for the sloppy screenshot, but it wouldn't paste the text neatly and I am tired AF)

  

The main problem being, there was no good way to figure out "k" (a 100 degree climb is not linear, it takes more time the higher we go) so instead I had to go with per fuel at a given temperature. If one of you math majors wants to come in and tell me I am an idiot and there was a far easier and accurate way to do this, I would love to hear it.

This is all extrapolated data from the wiki but it seems to jive with my own experiences. I've included this in my guide, but I know it is not of general interest to most of the community, but this data might be:

Smelting time is always 30 seconds per 20 nuggets (1 ingot worth)

Warm-up times,  Using the linear interpolation method based on the approximate data in the Vintage Story Wiki:

Fuel

Burn Temp

Low-Temp Metals*

Silver Solder (758C)1

Bismuth Bronze (850C)1

Molybdochalkos (902C)

Brass (920C)1

Tin Bronze (950C)1

Silver (961C)

Electrum (1010C)2

Black Bronze (1020C)1

Gold (1063C)

Copper (1084C)

Cupronickel (1171C)3

Nickel (1325C)3

Brown Coal

1100C

~0*

~0*

~42.5

~42.5

~42.5

~42.5

~54.0

~66.5

~74.5

~97.9

~102.8

N/A

N/A

Black Coal / Anthracite

1200C

~0*

~0*

~47.5

~47.5

~47.5

~47.5

~52.5

~56.5

~60.5

~64.6

~67.6

N/A

N/A

Charcoal

1300C

~0*

~0*

~45.0

~45.0

~45.0

~45.0

~48.5

~51.0

~54.0

~57.1

~58.4

N/A

N/A

Coke

1340C

~0*

~0*

~42.0

~42.0

~42.0

~42.0

~44.9

~47.2

~49.6

~51.9

~52.72

~75.4

~90.0

Important notes                                                                                                    
The asterisk (*) for metals with low melting points indicates that their estimated warmup times are likely very short (approaching zero seconds) with the hotter fuels. It's difficult to get a more precise reading within the resolution of the provided data. This includes Tin, Bismuth, Lead, and Zinc. Silver Solder might also fall into this category for the hottest fuels, but it's kept separate for slightly higher temperature.                                                                                                    
1 When creating alloys like Tin Bronze, Bismuth Bronze, Black Bronze, and Brass from nuggets, you need to reach the melting point of the highest-melting component (copper, 1084°C) to initiate the alloying process. The lower listed temperatures in the table represent the temperature at which already created ingots or bits of that specific alloy will remelt.                   
2 For Electrum, the highest melting point component is gold (1063°C), so you need to reach at least this temperature to create it from nuggets.                       
3 Brown coal, black coal, anthracite, and charcoal have maximum burn temperatures below 1325°C and thus cannot be used to melt nickel or create Cupronickel from nuggets.                          

Some take aways:                                                                         

Larger batches are more fuel efficient since there is a fixed overhead to heat the stack. I like to start with 4 peat and then add 1 charcoal + 3 for every 4 ingots worth, as it is ~30 seconds of fuel per ingot. Black coal you can do almost 3 ingots per. Brown probably closer to 2 (since it isn’t as hot). Anthracite about 6.

This works for copper, this works for any bronze. Also brass, gold, electrum, silver. Other lower temperature metals you’ll need less. Some you could get by with just peat or firewood.

Anthracite is overkill for preheating (but fine if you were going to smelt with it anyway). Don’t ever use coke for anything but nickel; it is just a net loss. You can start preheating nickel with peat or coal and then finish with 2 coke + 3 coke per 4 ingots.

Edited August 20, 2025 by Krougal
Some corrections

[Vratislav]

Nice overview.

From my experience, if you want to be especially thrifty with coal (as in early game ir if the coal is scarce), there is possibility to alternate coal with peat, as the crucible temperature stays for some time after reaching the top value despite heating temperature went lower.

BUT it is pretty tricky, I haven't found perfect pattern for this, as after the temperature reaches the top (1100°C or 1300°C for brown coal or charcoal), the time when the alloy keeps warm is declining. 

What worked was like

• 3x firewood - 2x peat - Brown coal - peat - then Brown coal, because further mixing is risky.
• 3x firewood - 2x peat - Brown coal - peat - charcoal - peat - charcoal - further peat is risky.
• 3x firewood - 2x peat - charcoal - peat - charcoal - peat - charcoal - further peat is risky.

For 3-5 ingots, these thrifty methods works quite well.

 

Edited August 20, 2025 by Vratislav

[Ryilo]

Nice work there, crunching all those numbers! 

I too usually start heating things up using peat, and I too found out that after reaching the smelting temps with coal using peat in-between can be risky, as at a certain point the temps lower below smelting temperature and it takes more coal to put it up again. Also, I hate to babysit it too much.

[Koobze]

Crunching all those numbers is some good work indeed!

I took the lazy way out and installed a mod that makes everything burn longer, so I put some charcoal on the fire along with my blend of metals and walk away, get distracted by a butterfly, go make dinner, go to sleep, and in the morning realize it's done smelting but the fire's still going and ready for the next load & distraction.

[Krougal]

Couple small corrections. Other redundant footnotes I missed. Also the warmup time obviously is significantly more than 0 for the low temp metals, but I kinda just let it go. Calling bullshit when the AI lies and correcting it is exhausting. If they don't know something, they will make up bullshit and waste hours of your time instead of just telling you it has no clue.

[Katherine K]

7 hours ago, Krougal said:

If they don't know something, they will make up bullshit and waste hours of your time instead of just telling you it has no clue.

They'll make stuff up even if it's within their training set, because they are trained on matching text, not semantics. You really shouldn't be delegating your thinking to LLMs. Not only is it making you worse at thinking due to not having as much practice (thinking is a bit like going to the gym in that aspect), you have absolutely no way of telling when you're getting good results.

That aside, the entire source code for smelting logic is public. Relevant function call:

public float changeTemperature(float fromTemp, float toTemp, float dt)
{
	float diff = Math.Abs(fromTemp - toTemp);
	dt = dt + dt * (diff / 28);
	// Various early outs if temperature is unchanged or reached maximum.
	return fromTemp + dt;
}

This function is used both to update the fire pit temperature and to update the temperature of the contents of the crucible. The difference is in how the dt parameter is supplied. For the fire pit temperature, dt is just the time tick. For the crucible, however:

float f = (1 + GameMath.Clamp((furnaceTemperature - oldTemp) / 30, 0, 1.6f)) * dt;
if (nowTemp >= meltingPoint) f /= 11;
float newTemp = changeTemperature(oldTemp, furnaceTemperature, f);

So in other words, the crucible heats up 2.6 times faster if the temperature difference between the furnace and the crucible is at least 48°C. Since that's practically always up to melting temperature, we can just run with that as the equation for the heat transfer:

dT/dt = 2.6 + 2.6 (Tₘₐₓ - T) / 28

Setting T = 0 at t = 0, and assuming your firepit has already warmed up, this can be solved analytically:

T = 2.6t + (1 - exp(-2.6t / 28)) Tₘₐₓ

So for example, here's copper heating up to its melting point of 1080°C in a little over 17s.

I've just tested this in survival, and it's pretty much spot on. I waited until the fire pit got to around 1280°C, added 20 copper nuggets to a crucible at that point and started the stopwatch. When copper reached 1080°C I stopped it. Stopwatch just rolled over past 18s. Given that I was a bit sloppy on timing, I'm pretty sure the extra second was me being slow on the stop watch.

Note that this assumes the firepit was hot. But so is the model you're quoting from Wikipedia that you fed into AI. So the numbers you got from AI are straight up wrong. Which should surprise absolutely nobody who knows how LLMs actually work. I suspect, it didn't even try to linearize the curve and just took the k as the slope, which is basically random garbage.

The reason this might feel like it's taking a lot longer is that people usually put the nuggets in first, then add the fuel and light it. That takes considerably longer, because fire pit has to heat up as well, and it heats up slowly, but also, the model is way more complicated. Especially, if you're juggling multiple different fuel types. Trying to estimate it with a line is just not going to work.

In summary, the numbers AI gave you are completely wrong and essentially made up. They are way larger than what they should be. The reason they feel right is because what you're doing is actually very different. You're waiting for the fire pit to heat up, not the metal. And since you're using different fuel types, the heat up portion is taking extra long. (It's still coal efficient, so that's fine.) The actual smelting time starting from cold fire pit being anywhere in the ballpark of AI numbers is pure coincidence.

I can put together the correct curves for heating up starting from cold fire pit with different choices of fuel combinations, if there's interest, but that will turn into a longer post, and I'll have to use Mathematica to make the plots. So let me know if anyone wants to see these.

[Krougal]

On 8/20/2025 at 5:41 PM, Katherine K said:

They'll make stuff up even if it's within their training set, because they are trained on matching text, not semantics. You really shouldn't be delegating your thinking to LLMs. Not only is it making you worse at thinking due to not having as much practice (thinking is a bit like going to the gym in that aspect), you have absolutely no way of telling when you're getting good results.

Too true!

On 8/20/2025 at 5:41 PM, Katherine K said:

That aside, the entire source code for smelting logic is public. Relevant function call:

public float changeTemperature(float fromTemp, float toTemp, float dt)
{
	float diff = Math.Abs(fromTemp - toTemp);
	dt = dt + dt * (diff / 28);
	// Various early outs if temperature is unchanged or reached maximum.
	return fromTemp + dt;
}

This function is used both to update the fire pit temperature and to update the temperature of the contents of the crucible. The difference is in how the dt parameter is supplied. For the fire pit temperature, dt is just the time tick. For the crucible, however:

float f = (1 + GameMath.Clamp((furnaceTemperature - oldTemp) / 30, 0, 1.6f)) * dt;
if (nowTemp >= meltingPoint) f /= 11;
float newTemp = changeTemperature(oldTemp, furnaceTemperature, f);

So in other words, the crucible heats up 2.6 times faster if the temperature difference between the furnace and the crucible is at least 48°C. Since that's practically always up to melting temperature, we can just run with that as the equation for the heat transfer:

dT/dt = 2.6 + 2.6 (Tₘₐₓ - T) / 28

Setting T = 0 at t = 0, and assuming your firepit has already warmed up, this can be solved analytically:

T = 2.6t + (1 - exp(-2.6t / 28)) Tₘₐₓ

I'm still a bit confused, partly because I've been away from this for 3 weeks, partly because I'm not so great at math to begin with.

Historically I tend to brute force my way through things. It used to work well for both physical and mental challenges alike, not so much anymore for either.

I did try to look through the source when I was doing this, but I don't even pretend to begin to understand those functions either.

On 8/20/2025 at 5:41 PM, Katherine K said:

So for example, here's copper heating up to its melting point of 1080°C in a little over 17s.

I've just tested this in survival, and it's pretty much spot on. I waited until the fire pit got to around 1280°C, added 20 copper nuggets to a crucible at that point and started the stopwatch. When copper reached 1080°C I stopped it. Stopwatch just rolled over past 18s. Given that I was a bit sloppy on timing, I'm pretty sure the extra second was me being slow on the stop watch.

Note that this assumes the firepit was hot. But so is the model you're quoting from Wikipedia that you fed into AI. So the numbers you got from AI are straight up wrong. Which should surprise absolutely nobody who knows how LLMs actually work. I suspect, it didn't even try to linearize the curve and just took the k as the slope, which is basically random garbage.

The reason this might feel like it's taking a lot longer is that people usually put the nuggets in first, then add the fuel and light it. That takes considerably longer, because fire pit has to heat up as well, and it heats up slowly, but also, the model is way more complicated. Especially, if you're juggling multiple different fuel types. Trying to estimate it with a line is just not going to work.

In summary, the numbers AI gave you are completely wrong and essentially made up. They are way larger than what they should be. The reason they feel right is because what you're doing is actually very different. You're waiting for the fire pit to heat up, not the metal. And since you're using different fuel types, the heat up portion is taking extra long. (It's still coal efficient, so that's fine.) The actual smelting time starting from cold fire pit being anywhere in the ballpark of AI numbers is pure coincidence.

I can put together the correct curves for heating up starting from cold fire pit with different choices of fuel combinations, if there's interest, but that will turn into a longer post, and I'll have to use Mathematica to make the plots. So let me know if anyone wants to see these.

So is this untrue? Smelting time is always 30 seconds per 20 nuggets (1 ingot worth)

I mean it wouldn't surprise me that something from the wiki is untrue either, but the melting time per ingot once the temperature has been reached does seem to be pretty consistent.

Oh, important to point out (because I maybe wasn't clear about it), I wound up NOT using any AI generated data in anything I posted. As I could not figure out any way to find "K" the formula was useless. As you pointed out, it is a bit complex and variable, so it doesn't look like there is any generic value for "K".

My more condensed useful (or at least what I thought was useful) section that I put in my guide:

These are your estimated warm-up times.

Fuel	Burn Temp	Copper (1084C)	Nickel (1325C)4
Brown Coal	1100C	~102.8	N/A
Black Coal / Anthracite	1200C	~67.6	N/A
Charcoal	1300C	~58.4	N/A
Coke	1340C	~52.72	~90.0

It seems to be ~accurate, or at least close enough for a rule of thumb, which is all I'm really trying to get at. That was heating time with ingots loaded. I've never thought to try heating an empty crucible.

As usual, I appreciate the insights from that sexy big brain of yours.

Maybe when I get over the jetlag it will make more sense to me.

[LadyWYT]

17 minutes ago, Krougal said:

Smelting time is always 30 seconds per 20 nuggets (1 ingot worth)

I mean, I haven't crunched the numbers or anything, but this feels right, at least for when the metal has come to temperature and begun to actually smelt. The time it takes to get it to an appropriate temperature though varies depending on what one is smelting; for alloys, the smelting temperature is whatever the highest required temperature is for the metals being smelted.

[Krougal]

Just now, LadyWYT said:

I mean, I haven't crunched the numbers or anything, but this feels right, at least for when the metal has come to temperature and begun to actually smelt. The time it takes to get it to an appropriate temperature though varies depending on what one is smelting; for alloys, the smelting temperature is whatever the highest required temperature is for the metals being smelted.

Yeah, that was why I considered copper and nickel the main things to worry about. The lower alloy temperatures really only come into play if you're smelting ingots back down and that just seems to be a waste of effort to me. Other than electrum; but then gold's melting point isn't that much lower than copper.

[Shoom]

I always pre-heat the crucible up to near 900 degrees with firewood and peat (usually 3 firewood + 1 peat OR just 4 peat if I'm feeling lazy)

Then I alternate between 1 charcoal and 1 peat until melting is done. I think using this as a rule of thumb is efficient enough, and most importantly it's fool proof, as long as you don't walk away, this will save you some coal while getting the metal melted.

If I melt using brown coal I don't bother to micro-manage since the burn time is so long and the burn temp is too close to copper's melting point for comfort, any mistake here basically forces you to start over.

I use brown coal as my "light and forget" fuel for when I'm multi-tasking around the house/yard and don't want to bother micro-managing.

As for black coal, I haven't found enough of it to figure out what to use it for.

Side note; I wish there was a block that functioned like a crucible/campfire which you could route chutes and hoppers into

[Krougal]

5 hours ago, Shoom said:

I always pre-heat the crucible up to near 900 degrees with firewood and peat (usually 3 firewood + 1 peat OR just 4 peat if I'm feeling lazy)

Then I alternate between 1 charcoal and 1 peat until melting is done. I think using this as a rule of thumb is efficient enough, and most importantly it's fool proof, as long as you don't walk away, this will save you some coal while getting the metal melted.

If I melt using brown coal I don't bother to micro-manage since the burn time is so long and the burn temp is too close to copper's melting point for comfort, any mistake here basically forces you to start over.

I use brown coal as my "light and forget" fuel for when I'm multi-tasking around the house/yard and don't want to bother micro-managing.

As for black coal, I haven't found enough of it to figure out what to use it for.

Side note; I wish there was a block that functioned like a crucible/campfire which you could route chutes and hoppers into

Oof! That is some micromanagement hell right there. That is exactly what I am trying to avoid and why I started trying to crunch numbers.

So you are letting the temperature drop, but not enough for the metal to stop melting, which makes sense in theory but:

1 charcoal and 1 peat, ~2 ingots.

1C+1P+1C+1P or just slap in 3C ~4 ingots and walk away.

The micromanagement only gets worse the more ingots you are doing at once. I mean granted, you still have to hang around and not get too involved in other shit lest the whole thing cool off on you before you can pour, so it isn't that big a deal. 

Black coal burns for 84 seconds at 1200C, ~3 ingots.

Granted this is still off the assumption of 30 seconds per ingot, I haven't had a chance to try Kat's method of heating the empty crucible.

I also use https://mods.vintagestory.at/betterfirepit which I am not sure if/how it interacts with smelting. I don't think it does, but I figured it bears mentioning.

Oh, and I misspoke earlier when I said I didn't use any of the AI drivel, I obviously didn't arrive at 0 seconds warm-up time myself, so that big chart is it.

Actually looking over Kat's plot again, and having had sleep and coffee, 17s isn't that far off 20s, especially as we know the fuel temperature vs the melting temperature is going to throw that off; the 20s is a really rough estimate. I think the difference if you preheat with the nuggets or not has no real impact, other than adding more micro.

Ideally I want to know how much fuel to shove in, load it, light it, and set a timer so I can go do something other than stand there with my thumb up my ass but not have it cool down before I can pour. In theory 2 charcoal should pre-heat, which is better than 4 peat + 1 charcoal, although as Kat said, those numbers are highly suspect.

Edited September 10, 2025 by Krougal

[Shoom]

1 hour ago, Krougal said:

So you are letting the temperature drop, but not enough for the metal to stop melting, which makes sense in theory but:

Only the temperature of the fire drops, 1 peat has short enough burn time for the temperature of the metal to remain at 1300°C

So if the theory is correct, the peat should practically be extending 1 charcoal's effective burn time by 25 seconds, so you should be saving quite a bit of charcoal in the long run which means less tree-chopping and charcoal pit-making which is more tedious in my opinion than micro-managing crucibles, just personal preference.

I could be wrong however, perhaps the fire's temperature affects the melting rate as well? I haven't done any math on this or looked at any code, this all just stems from gut feeling.

 

[LadyWYT]

6 hours ago, Shoom said:

I use brown coal as my "light and forget" fuel for when I'm multi-tasking around the house/yard and don't want to bother micro-managing.

As for black coal, I haven't found enough of it to figure out what to use it for.

That's what I use black coal for, since it has about twice the burn time of brown coal. Brown coal is more comparable to charcoal, but doesn't burn as hot. I also don't really worry about brown coal usage as much since it tends to be rather easy to find.

[Shoom]

10 minutes ago, LadyWYT said:

That's what I use black coal for, since it has about twice the burn time of brown coal. Brown coal is more comparable to charcoal, but doesn't burn as hot. I also don't really worry about brown coal usage as much since it tends to be rather easy to find.

Thanks, brown coal seems a LOT easier to find indeed, I believe all my black coal stems from ore vessels, I've found several brown coal veins and have crates filled with the stuff, black coal on the other hand I only have a measly 20 pieces or so of so I'm afraid of using it. 

[Krougal]

Brown coal is good to use as fuel for steel, since unless you use https://mods.vintagestory.at/show/mod/22009 , it doesn't matter what you use. With the mod, anthracite becomes very efficient. Black coal next.

It is also good to use for coke, while black coal is more efficient at making coke, it is also rarer and more useful in general. Currently, you also only need enough coke for smelting nickel, so it isn't worth going crazy making in excess.

You can also use black for carburization instead of charcoal. It's also used for dye and ore bombs; so yes, it is worth using something else as fuel when possible.

Edited September 10, 2025 by Krougal

[Shoom]

2 minutes ago, Krougal said:

Brown coal is good to use as fuel for steel, since unless you use https://mods.vintagestory.at/show/mod/22009 , it doesn't matter what you use. With the mod, anthracite becomes very efficient.

It is also good to use for coke, while black coal is more efficient at making coke, it is also rarer and more useful in general. Currently, you also only need enough coke for smelting nickel, so it isn't worth going crazy making in excess.

 

 

I heard a rumor sometime ago, saying that you if put a iron hatch underneath a cementation furnace and build the cementation furnace base out of refractory bricks it will double as a coke oven so any coal put in there to fuel the cementation furnace will turn into coke while burning, I haven't tested it myself and I don't know if it's of any use but I thought it was a cool thing. 

[Krougal]

3 minutes ago, Shoom said:

I heard a rumor sometime ago, saying that you if put a iron hatch underneath a cementation furnace and build the cementation furnace base out of refractory bricks it will double as a coke oven so any coal put in there to fuel the cementation furnace will turn into coke while burning, I haven't tested it myself and I don't know if it's of any use but I thought it was a cool thing. 

Interesting. I've never heard that, I doubt it though, the coke oven only has room for 1 stack of coal and the cementation furnace requires both spots under the coffin to have fuel. The grid that would be the top of the coke oven are also gratings, which I don't think are valid. Even if it worked, I wouldn't count on it not being patched out (or maybe it did work and has already been) as it is seems (for all I know it could work like that IRL) like an exploit.