For the purposes of this question the builders are incredibly wealthy, have access to cheap nukes to use for excavation, and everyone in this world is immune to radiation.

The technology is decades ahead: but no Clarktech is supposed to be used here, just stuff like lots of nukes, and automation to create the ceramics that line the molds the magma will be made to flow into. So you'd basically be building a larger hollow version of the structure out of, or at least lined with ceramic. Which the magma is injection molded into by its own pressure before the ceramic and any heating elements are finally removed after cooling.

Getting access to a magma chamber from a dormant volcano is possible, but ideally people would just use their plentiful nukes to blast deep enough into the crust that they aren't beholden to the local geology.

This isn't intended to be the most pragmatic method of construction by a long shot, but it seems like by controlling the rate of cooling you could create some truly beautiful buildings injection molded with igneous rock. Plus you could texture it however you want by shaping the ceramic plates of the mold. Though depending on specifics the rock may still need to be polished first anyway (though if the rock didn't touch the air while cooling against a smooth surface maybe it would already be basically polished?).

Is this idea actually workable? Can one truly injection mold palaces out of rock, or perhaps even crystal like obsidian?

  • $\begingroup$ your real problem is building a mold that can survive detonating a nuke inside it. Also you have no way to turn the lava off, if it has enough pressure to erupt it will keep erupting. $\endgroup$
    – John
    May 16, 2023 at 23:08
  • $\begingroup$ @John I was imagining you wouldn't connect the mold to the borehole until it was already blasted and the magma was rushing up. Also you could blast most of the borehole but then manually excavated some portions so as to install something like a valve. $\endgroup$ May 16, 2023 at 23:54
  • $\begingroup$ This reminds me of a video I saw recently on YouTube of an attempt to cast an obsidian sword. Spoiler: It doesn't work great, but then again he wasn't using nukes. $\endgroup$
    – Atog
    May 17, 2023 at 17:42
  • $\begingroup$ @VakusDrake you do a valve with lava it it is cold enough ot be solid ot is cold enough for the lava to solidify inside it. $\endgroup$
    – John
    May 17, 2023 at 20:15
  • $\begingroup$ @John I'm imagining you make a valve out of say tungsten carbide or ceramic and heat it enough to keep the magma flowing without deforming the valve material. After all there's a decent different between the melting point of many materials and that of magma $\endgroup$ May 17, 2023 at 20:23

2 Answers 2


Frame challenge: Lava 3D printer


  1. You have to build an oversized copy as a mold. This is a huge amount of resources, and lots of work to construct and deconstruct afterward.
  2. This will not be able to build all internal structures like floors, walls, etc. in a single pass. Complex objects are often made from multiple injection molded parts.
  3. I assume you will need a lot of nuke to cause volcanic activity. Uranium enrichment ain't cheap.
  4. If you are dropping nukes in the mantle to cause volcanos, a lot of the energy is going to be absorbed into the mantle in all directions. How do you make sure that volcanic activity happens where your giant mold is?

I think a 3D lava printer would yield better palaces for cheaper, and would be practically achievable earlier in a civilization simply due to the reduced scale of the forces and materials.


Obsidian is basically glass. The chemical composition of Obsidian is anywhere from 65-80% Silicon Dioxide - glass. If you can mold your buildings out of glass, then you can mold them out of Obsidian. SiO2 melts somewhere around 1,700 degrees F. However, experiments reported bubbling at lower temperatures https://chemistry.stackexchange.com/questions/74534/melting-point-of-obsidian .

You won't need a nuke to do this. A gas furnace can get hot enough. https://en.wikipedia.org/wiki/Glass_melting_furnace


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