I might be wrong, but I remember reading that aluminium is one of the least likely elements to be available in a pure form on a planet. It wasn’t until modern industry that we could get large amounts of aluminium available to us. I remember reading that in 1700s nobles in France used aluminium cutlery because it was more expensive than gold.
You may be refering to titanium or something because as far as I know, aluminium is the most abundant metallic material and is the third most common of all elements, oxygen and silicon coming first. I also remember reading abundance in metalic material increases underwater.
I’m pretty sure it is aluminium. Found some links that say it is difficult to extract aluminium (even though it is very abundant in overall amount):
(testing reply by email)
Well the main focus is getting either these already made slates from around black smoker vents which are hot enough to melt metal internally and combine them with sulfur (which is why they produce the black smoke) and just crush the bits up and purify with chemical leaching, or you can get bauxite ore in itself, chip away at the much softer rock, and corrode and leach that away.
(Edit: No I am not saying to use hydrothermal vents to smeltal the meltals, I’m saying to use the metalic soot layers around it and refine it/ filter it into the necessary powders for thermite which will then skeletal the metals)
Well that didn’t work too well. Here are the links I found:
https://www.studyrankersonline.com/62555/why-extraction-of-aluminium-is-difficult
Good luck with that, it looks like aluminium is almost a hundred (actually I maybe misread it, maybe it was just 10 times) times harder (in terms of energy when comparing to steel manufacturing) to melt.
I’m tired of people suggesting a solution first, and only afterwards thinking how you get that solution. This is why the underwater threads keep getting locked.
You need to start any explanation from nothing except what you can find underwater naturally.
Yeah, you are right, I got carried away with the evidence and got ahead of myself with sporadic thoughts I was getting. I’ll attempt this again trying to conclude the problem before the solution. Underwater technology of any sort sounds it will be drastically different, and we know the main problem is water separating the fire triangle to numb any combustion or melting. This makes the best bet to remove any water. Lets assume these aliens live in a full water world (with an ocean floor, not one of those condensed ice super giants). This makes any sort of removing water from the equation really really hard. Starting off, since there is no metal yet and we can not use electricity we have to assume everything we use will be either manually mechanical, chemically controlled, or controlled by means of physical logic. Starting off, how do we contain any sort of pocket of air underwater? Well, any fluid pocket in another fluid will easily be contained as long as there is something to hold it in. You can demonstrate this using a cup, turning it upside down and then submerging it underwater. If you put this cup a lot further downwards, maybe in a deep swimming pool, you’ll notice this water compresses due to water pressures squeezing any air in. Now this is a challenge because it means the deeper in water level your civilization is emerging from, the harder it is to sustain enough air in whatever area you have. Funny enough, this air compression problem has a use in a device called a trope, which is a water powered air compressor used in Bloomberg furnaces, which a furnace was our goal in the first place, yet I would assume a trompe would not work underwater. Using logic of physics this air column would seek to match the pressure of the surrounding water, which increases 100 bar for every 1 kilometer I think. 100 bar is quite a bit, and so pressurizing this air and supplying it in increments would be pretty hard. I say we fix this by having a stable flow of continuous air, which would probably be done by turbines. Turbines in the conventional sense use electricity and electromagnetism to spin, but perhaps it would be possible to either manually spin it with gears or spin above the surface with something similar to a rocket motor (I request putting oil from oil leaks to flow into a tube and then igniting it). This enclosed space with air flow in and out will be the first step to a furnace. Any ideas that may help air flow get in (getting out is quite easy if you have two tubes) or anything that disputes any of the two methods I have stated, please feel free to describe so.
[Edit: It took me so long to write this because I had to go outside of my house for a bit]
Ok wow people can come up with so many ideas! And this is a good one. It might work, but the simple question of why in all hell would a premetal civilization do this puts a dent in it. I will try to think of some ideas, bit I must recommend puting yourself in the mindset of a specific civ. They may have a different mimdset then humans, so I recommend finding one condusive to this idea, and seeing why they would evolve it.
Asking why an alien did something if they have vastly different motives and intentions to us is a bit dumb and I can also ask why in the hell would a human try cooking rocks over a fire? I suppose after stable settlement they would want to experiment with things around them, air being one. They then see some of its uses and regularly use air for some specialized applications until a furnace is idealised.
Hmm, well humans had found that if a spear had been heated it was harder, so when they found soft metals and made spears out of them they did the same. The thing was, it did the opposite and made the metal softer! This was easier to sharpen and shape, and it wore of. They tired with progressively hoter fires and the metal melted. Why did they do this? They were curious. What chain of events might parallel this under water?
I don’t want to go back and forth again, but how in god’s name did they figure that heating a spear
would make it stronger??? Also as to your question it’d be the same as humans, curiosity propelling them to test out things that they know little about.
Because some clumsy cave person dropped a spear in the fire and it came out harder. Well I think we have the reason, but this is still a high resource endeavor. Why make giant tube with turbines when you can just not? I think maybe if tubes or something had a more obvious use that can be adapted, it would make more sense. I mean, human had spears fire and air already. All they added was metal. Also what if they tamed electric eel analogues to electrolize water? The oxygen and hydrogen could gather in a diving bell. I don’t think the hydrogen could combust nearly hot enough but it could be a gateway step.
Can fire burn in an atmosphere of oxygenated water-vapour? And if so, could this allow a fully underwater smelter of some sort?
Is not the same thing as
I meant that the smelter-structure could be fully surrounded by water, without needing to be connected to a natural source of air
How would that work?
Here’s and idea to test it: turn on your whatever-you-use-to-make-tea and wait for it to make lots of steam. Light a match and hold it our into the steam. Note that if the match doesn’t go out that doesn’t mean pure water vapor would work, the main point of this is to disprove the idea, not to prove it. I think that it might work, but I haven’t tested it.
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Yeah you are right. What the 
is oxygenated vapour supposed to mean though?
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So if you lower the pressure or raise the tempature in a system to the point that water cannot maintain liquid form, then introduce water, you get water vapor. This would be a whole lot easier to get underwater then N2, and O2 would naturally diffuse into the vapor. The question is: does replacing N2 with H20 disrupt the fire process? I would also like to point out that water hampers fire with it’s abilitiy to hold heat. This steals heat from fire and can disrupt it. I don’t know if this is negligible or can be dealt with.
Methane and oxygen trapped in ice pockets during early formation of everything as well as oil pockets. Has this been brought up before?
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Even if a creature can obtain this methane, it may not be possible for them to make an underwater smelter