This question is supplementary to the following LEGO™ as a defence against barefoot warriors

One answer suggests making weapons and other artifacts by melting and moulding LEGO plastic (ABS).

Is this in fact possible using only neolithic technology?


  1. There are no metal containers during the neolithic

  2. ABS thrown on a fire will burn before it has time to melt and form a puddle

  3. I don't know if neolithic pottery could be used as containers for melting and moulding. If so, could they protect against the plastic catching alight?


Acrylonitrile Butadiene Styrene, or ABS, is an opaque thermoplastic. It is an amorphous polymer comprised of three monomers, acrylonitrile, butadiene and styrene. ABS is most commonly polymerised through the emulsification process or the expert art of combining multiple products that don’t typically combine into a single product. https://www.adrecoplastics.co.uk/abs-plastic-properties-and-application/

Early Neolithic farming was limited to a narrow range of plants, both wild and domesticated, which included einkorn wheat, millet and spelt, and the keeping of dogs, sheep and goats. By about 6900–6400 BC, it included domesticated cattle and pigs, the establishment of permanently or seasonally inhabited settlements, and the use of pottery. https://en.wikipedia.org/wiki/Neolithic

LEGO Toys On FIRE video

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    $\begingroup$ brb, putting ABS plastic in a ceramic bowl (under water) on the BBQ. $\endgroup$
    – Ash
    Aug 29 '20 at 15:04
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    $\begingroup$ Aren't Lego pieces make by injection moulding? I'm sure they can melt ABS plastic with Neolithic technology (its glass transition is at temperatures just a little above the boiling point of water, so that carefully heating it in a stone or ceramic pot ought to do it fine), but I am also sure that they cannot make the injection moulding equipment. As far as I know, molten ABS is very viscous, and won't flow into the mould unless pumped under pressure. On the other hand, ABS is lightweight and soft, not ideal qualities for weapon materials. $\endgroup$
    – AlexP
    Aug 29 '20 at 17:23
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    $\begingroup$ @Alex it can be pressed into a shape using simple wooden plates, you are not going to get complex shapes but you can boil it to reshape it after melting it. $\endgroup$
    – John
    Aug 29 '20 at 18:19
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    $\begingroup$ "Accurately?" You should look up just how accurately they machine the tooling that is used to make LEGO bricks. It's astonishing: It's much more precise than you would expect for any plastic toy. But, that's to control their ability to fit together, to stay together, and to come apart again when (and only when) you want them to do. Sounds like you wouldn't really care about that so much. $\endgroup$ Aug 30 '20 at 16:05
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    $\begingroup$ @warren - Availability is assumed in this question. If you want to know why it is assumed, the explanation is given in my previous question - worldbuilding.stackexchange.com/questions/184560/… $\endgroup$ Aug 31 '20 at 15:18

Let's try it and see!

So I didnt have any Lego bricks free, So I used abs 1.75mm filament from my 3d printer, (which is thicker than the wall of a Lego brick so actually harder to melt)

I put it on a ceramic plate on my bbq (fire and ceramic are both neolithic), and it melts down to a sticky blob. I'm able to form it with other ceramic tools (buts of broken tile I found in my backyard) but lack a mould to try to get a perfect shape.

However the stickiness makes it really easy to work with with basic hand tools, sort of like glass blowing when you use wet newspaper to shape it with your hands. just using a ceramic tile I was able to mould a plausible first attempt at an arrow head. With practice I expect I could do a lot better.

Experimental setup. A plate, a bbq, some chunks of broken roof tile, and abs plastic from my 3D printer:

enter image description here

And here's as good as I was able to get it in a few minutes of my first attempt at shaping moulten plastic by hand:

enter image description here

I wasn't able to the get tip sharp on my first attempt, but it's sharp on the sides there.

Using a proper "Mould" may actually be harder than just shaping it using hand tools, as it is sticky and you'll need to push it into the mould with some pressure to get it fully sharp. But I'd say totally possible to melt and shape ABS plastic using only ceramic and fire.

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    $\begingroup$ Marvelous effort to answer! $\endgroup$
    – Mary
    Aug 29 '20 at 15:54
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    $\begingroup$ youtube.com/watch?v=j6veqON60IE remolding scrap ABS. the key is low and slow. more like baking than roasting. $\endgroup$
    – John
    Aug 29 '20 at 18:18


My son has a plastic curly drinking straw. I discovered the hard way that it becomes ductile at somewhere less than 100 degC when it went through the dishwasher the first time. All was not lost though - I dunked it in boiling water repeatedly to reshape it.

Ash in his answer has made the classic mistake of using an uncontrolled temperature, namely a barbecue plate. The result is significant amounts of burning instead of just melting. Liquids boil at a (relatively) well-defined temperature, so finding a suitable liquid to boil will allow your cavemen to melt the Lego without burning it. Checking Google,ABS becomes ductile at 40-80 degC, and actually melts at 190-270 degC.

So the first option is simply to use boiling water for reshaping as I did. Smiths do not melt iron and steel, they simply heat bars until they're ductile and then shape them as required. Glass blowers work in exactly the same way. There's no reason you couldn't use this to construct any ABS shape you want. It will tend to suffer from imperfect joins if you try to weld two pieces together, of course.

If you do want to actually melt it though, use animal fat. The smoke point of beef fat is around 200 degC, but if you render it to tallow then the boiling point of that is 338 degc. Plenty hot enough to melt your ABS, but not hot enough to burn it.

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    $\begingroup$ Neolithic people could safely get boiling water by partly filling a water-proof box or basket, and adding stones heated in a fire. $\endgroup$ Aug 30 '20 at 7:54
  • $\begingroup$ @PatriciaShanahan Yes, I was kind of taking for granted that they'd have mastered fire and cooking, otherwise it becomes pretty hard to manage. (We have a shortage of hot volcanic springs at most Legolands!) It's good to fill in those details though. $\endgroup$
    – Graham
    Aug 30 '20 at 20:15

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