I am trying to recreate King Arthur's the Sword in the Stone using chemistry.

I have a couple ideas how this could be done Would any of these work or how it might work? enter image description here Arthur removes the sword from the stone and is blessed by Archbishop Brice, from Le Livre de Merlin, France, N. (Arras), 1310, Add MS 38117, f. 73v." Caption via the British Library's Medieval Manuscripts Blog.

Unlike this answer: Making a sword in the stone, in a medieval world without magic I am interested how this could have been done with a substance available in 500AD.

What could be smelted or concreted then to allow a sword to be entered into it then allowed to cool or harden with no chemical bond to the sword?

The material of the stone would need to contract as it gets colder to release the sword at a certain temperature, not be so hot during insertion to effect the temper of the sword, and/or allow water or ice to permeate between the sword and stone.

Similar to using whiteout to create a barrier between the soft iron shell and the inside hard steel of a canister Damascus forge could the sword be coated with a whiteout/liquid paper like material that breaks down when wet over time?

enter image description here An eight-year-old found a pre-Viking-era sword while swimming in a lake in Sweden during the summer. It is relativity intact for being in the water that long. Source: https://www.bbc.com/news/world-europe-45753455

Could water get between a designer stone and the treated sword enough to erode or breakdown the bond between the sword and the stone with little corrosion to the sword?

The simplest way this could be done I can think of is thrusting the sword into a ball of lava rock that meets the edge of an ocean then moved and carved. Over time water and winter loosen the sword.

enter image description here

  • $\begingroup$ Could you please include a clear definition of what you mean by "whiteout"? When I look it up, it just comes up with a load of film references. That product may not be available in all the countries that our members live in. Can you clarify please? Also, are you asserting that the sword is not corrosion resistant, like just a normal steel sword, what's to stop atmospheric moisture from corroding the tang and expanding to destroy the handle? $\endgroup$ – BLT-Bub Jul 27 '19 at 18:40
  • $\begingroup$ ...Cont. At the moment your question seems to be story based and has little to do with worldbuilding. It would perhaps help if you provided context that gave us the worldbuilding problem in a nutshell. $\endgroup$ – BLT-Bub Jul 27 '19 at 18:49
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    $\begingroup$ @Confoundedbybeigefish. Whiteout is a generic term for liquid paper often known by the brand name Tipex. The white fluid painted onto paper to correct spelling mistakes when typing or writing by hand. There is an American TV show called Forged in Fire that has highlighted its use in the sword making process. $\endgroup$ – Sarriesfan Jul 27 '19 at 19:36
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    $\begingroup$ Sticking the sword in lava will ruin the temper of the steel, Getting steel more than a few hundred degrees will ruin the temper. $\endgroup$ – John Jul 27 '19 at 19:38
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    $\begingroup$ Whiteout will have no effect on the heat ruining the temper of the steel. en.wikipedia.org/wiki/Tempering_(metallurgy) $\endgroup$ – John Jul 27 '19 at 19:44

You could use Roman concrete


Roman concrete, also called opus caementicium, was a material used in construction during the late Roman Republic until the fading of the Roman Empire. Roman concrete was based on a hydraulic-setting cement. Recently, it has been found that it materially differs in several ways from modern concrete which is based on Portland cement. Roman concrete is durable due to its incorporation of volcanic ash, which prevents cracks from spreading... Further innovative developments in the material, called the Concrete Revolution, contributed to structurally complicated forms, such as the Pantheon dome, the world's largest and oldest unreinforced concrete dome.

The Pantheon is 2000 years old and looking very, very good. Roman concrete is poured and cast like modern concrete, but is chemically different from modern concrete in several ways. If you are materials-science inclined, recent studies of Roman concrete make for interesting reading. To release the sword the concrete does not contract, but the metallic sword does. It needs to get really cold.

Your sword is embedded in Roman concrete and has been since Roman-trained engineers put it there 150 years before your story. Dark ages medieval Britons would know of the Romans and be familiar with their works but would likely have lost the arts of reproducing their technology - which is what really happened.

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    $\begingroup$ For added spice, the way the Romans make concrete used materials not found on the British Isles, specifically pozzolanic ash, which is a sort of natural cement. So there was no reason for Britons to remember how make concrete -- they did not have raw materials anyway. The sword-in-stone must have been set up with imported materials. $\endgroup$ – AlexP Jul 27 '19 at 19:20
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    $\begingroup$ @AlexP: Example: the seawall in Roman Palestine. en.wikipedia.org/wiki/Caesarea_Maritima#Construction_techniques And in the text: "Herod imported over 24,000 m3 of pozzolana from the name-giving town of Putoli, today Puzzoli in Italy, to construct the two breakwaters:" So you are right - imported ash. $\endgroup$ – Willk Jul 27 '19 at 20:13
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    $\begingroup$ Great example, and good confirmation that indeed they were perfectly able to import natural cement when they need and wanted to. Ties in with the answer, too! $\endgroup$ – AlexP Jul 27 '19 at 20:17
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    $\begingroup$ @Muze: "How much roman stuff is found outside Italy at that time?" Quite a lot. Lots and lots. By the 1st century CE the vast majority of the Romans were not Italiots/Italians anyway. That's the entire idea of an "empire". (And this is where most modern empires failed. In a successful empire one doesn't go about making petty distinctions between people from the original provinces and people from other provinces. Once you got around and conquered Hispania and Syria you should make sure that Hispanians and Syrians can become senators, generals and emperors just like anybody else.) $\endgroup$ – AlexP Jul 27 '19 at 20:20
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    $\begingroup$ "Any sufficiently advanced materials science is indistinguishable from magic" - or something like that... :-) $\endgroup$ – Bob Jarvis - Reinstate Monica Jul 28 '19 at 4:12

I am trying to recreate King Arthur's the Sword in the Stone using chemistry


You could use thixotropism and come up with a sword that cannot be removed from its stone scabbard no matter how hard you pull, unless the sword is rattled gently for a couple of minutes beforehand. However, this solution is almost surely bound to undergo degradation along the years.


The simplest way to reproduce the effect would be with a friction lock. Basically, the Stone has a wide hollow "sleeve" inside, not so large as to perceivably alter the Stone's mass or balance; the sleeve is drilled from the bottom side of the Stone and stops a few inches from the surface of the top side, where it narrows to the exact width and thickness of the Sword's blade. So, from above, the Sword is set in the Stone. If this was the whole setup, the Sword would be very easy to extract.

But inside the sleeve you have two steel prongs as long as the blade, covered with a layer of soft lead. Once pressed against the blade, the blade bites the lead and leaves its exact impression; if the rods are kept pressed hard against the blade, the friction is so high that you will never be able to extract the blade, not even using levers. You'd break the blade hilt first.

Now the prongs are kept in place by a counterweight mechanism hosted in a small chamber beneath the stone. The mechanism can work in several ways: it can be "remote-controlled" from a nearby cloister through a wire or light chain pulled through a tube, or it can be released by placing weight on specific stones. One could even devise a "combination lock" so that you'd need to put your weight on stone A, then B, then A, then C, then B to achieve release. Of course anyone would feel the pavement stones wobble slightly, but if most of the flagstones were equally wobbly, nobody would think twice about it. If the mechanism were controlled by pulling a pin attached to an underground chain in a tube, even the wielder of the Sword would never know how the trick was done.


enter image description here

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    $\begingroup$ Thixotropism... so it's held in place by ketchup? $\endgroup$ – DrSheldon Jul 28 '19 at 3:16
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    $\begingroup$ @DrSheldon from the great hot dog to the great hot dog he goes. $\endgroup$ – Robert Columbia Jul 28 '19 at 11:24

Gypsum. Also known as drywall. Gypsum plaster has been used for millennia. https://www.youtube.com/watch?v=tmbk8Pfau0I

With a little artistry, you could easily cast it into the shape of a big rock around a sword. Throw in some darker sand/gravel and maybe some bigger stones, to give the appearance of natural occlusions.

The big advantage gypsum has over concrete is that it's not all that strong. A big guy could possibly pull a sword out, whereas I'd think cement/concrete would be impossible. The sword in that case is basically rebar.


We can take advantage of the fact that when dissimilar materials are in contact, they will typically have differing coefficients of thermal expansion.

Basically, as solid objects get hotter, they expand, and they contract as they get cooler. The difference between the coefficients of the materials involved can be used to create a system that will release the blade under the appropriate thermal conditions.

Steel has a coefficient of expansion of around 12 nm/mK. Granite, a common, hard, weather-resistant stone has a coefficient of expansion of around 7.9 nm/mK.

This means that for every linear metre of the substance, for every degree Kelvin that its temperature increases, it will expand x nanometres.

The problem is that 7.9 and 12 are quite similar... the difference is only 4.1nm/mK, meaning that quite a large negative temperature differential would be required to cause the sword to release from the stone.


The system need not be mechanically so simple as a sword in a blade-shaped hole in a solid block of granite requiring a significant, prolonged, drop in temperature to cause the blade to contract sufficiently to release from the stone.

If we were to have two blocks of granite, each forming half of a vertical cylinder split vertically through its diameter, with a blade-shaped notch in each side, so that with the sword between them, the stones don't quite meet, held together by a circular steel strap, like the steel tyre on a wooden wagon wheel, we would have a system where a relatively small increase in temperature would result in a relatively great expansion of the steel strap (because it is much longer, by a factor of Pi×Diameter than the gap between the stones). This would allow us to create a system where the sword would become loose at or above a specific temperature. By surrounding the stone with a fire, the strap could be made to expand enough, while ordinary daytime temperatures would not, or the strap could be sized to release only on the hottest of daytime temperatures.

This would also have the advantage that rhe sword would not become blunted by its compression in the stone(s), and it could be preserved from rust by filling the gap between stones with a resin.

All of this is easily achievable with iron age technology.

The steel strap could be embossed to make it look decorative, rather than the key piece of the lock, so only a wheelwright pr perhaps a blacksmith would likely consider the mechanism by which the sword might be released... and in the middle ages, knights didn't soil their hands with manual labour, or bother themselves to understand what it is that craftsmen do.

Knights guard the stone, and will allow only another knight to approach... so only a knight who actually thinks about the common people is likely to figure it out or be popular enough and receptive enough to be told and listen.

  • $\begingroup$ cutting a precise sword shaped hole in granite is unfortunately not achievable with iron age technology. $\endgroup$ – John Jul 28 '19 at 3:50
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    $\begingroup$ Of course it is @John. It need not be too precise, since that is what the slight gap between the stones is for. It is not a hole in the stones, it is a notch on the sides of two stones. Easy to achieve with a hammer and chisel. $\endgroup$ – Monty Wild Jul 28 '19 at 3:51
  • $\begingroup$ Not with a chisel but you can saw stone easily enough as long as you are patient, $\endgroup$ – John Jul 28 '19 at 3:53
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    $\begingroup$ The ancient Egyptians could do it, any mason could do it in the middle ages. Masonry was how stone castles and bridges were built . $\endgroup$ – Monty Wild Jul 28 '19 at 3:56
  • $\begingroup$ The egyptians used saws, the invented the ox powered reciprocating saw., chisels have a minimum gap you need to cut deeply with. For one thing the chisel needs to be wide enough to have the necessary strength and that is quite a bit wider than a sword. $\endgroup$ – John Jul 28 '19 at 4:00

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