Maridinium is a made-up metal of my own creation. It's defining property is that it has a high volume expansion coefficient. Meaning it expands when heated much more than normal metal.

Notable Properties:

  • High Volume Expansion Coefficient (Cb = 0.01), it will expand much more when heated than metals normally.
  • High Thermal Conductivity (So it is easier to heat it thoroughly instead of heating one area)
  • Low Melting Point (260 Celsius)
  • As strong as iron
  • Slightly more malleable than bronze
  • Dark Silver Colored
  • Rust Resistant
  • Non-toxic

Now say the Romans in 0 BC/AD had access to Maridinium. With its properties, what are some potential applications of this metal?

*Edit: To clarify how much the metal expands, the Cb means that for every degree Celsius that one cubic meter of the metal is heated, it expands 0.01 cubic meters(or 1 cubic centimeter), I think the equation is:

[Change in Volume] = Cb * [starting volume] * [Change in temperature]

In other words, when some cold maridinium(0 C) is placed in boiling water for a while, it will double its volume.

  • $\begingroup$ You'll never have an industrial revolution with this metal. However, it will be a reasonable substitute for iron in many of the applications the Romans and Roman-era people would have for metal. Swords and knives, small scale mechanics (buckles for harnesses or whatever). Assuming it is cheap enough to produce in bulk. $\endgroup$
    – John O
    Commented Dec 9, 2022 at 21:43
  • $\begingroup$ Does it shrink back down when cooled? $\endgroup$
    – Daniel B
    Commented Dec 10, 2022 at 22:07
  • $\begingroup$ Yes, metal expands when heated and shrinks when cooled, Maridinium does that also, just the degree at which it does it much more extreme $\endgroup$
    – KaffeeByte
    Commented Dec 10, 2022 at 22:19
  • 2
    $\begingroup$ VTC: this question seems too open-ended: "what are some potential applications." How could a single answer be selected as best? $\endgroup$
    – Tom
    Commented Dec 10, 2022 at 22:41
  • $\begingroup$ Correct me if I'm wrong, but if its Youngs modulus is similar to bronze, the thermal expansion of maridinium also implies an incredibly high thermal capacity, doesn't it? $\endgroup$
    – user86462
    Commented Dec 12, 2022 at 10:25

5 Answers 5


One application would be its potential use for building materials.

An ancient way of splitting a very large stone was to chisel out a deep groove and push wooden wedges into it. The wood was then wet down, causing it to expand. Eventually, with enough wet wedges placed into the correctly positioned grooves, the stone would split. If your metal is strong but malleable, it would be easy to form reusable wedges for splitting wood, and would be quicker and less labor intensive to split stone used for building, road materials, etc; quicker because it could expand quickly with it's high conductivity, and less labor intensive as no one would be needed to continuously wet the metal as was needed for the wooden wedges.

It might make a good material for coins, as it could not as easily be adulterated. An expandable coin is relatively easy to test for purity. The use of the coin, if the metal was not inherently valuable, would need to be backed up by something of value, and attempted adulteration would need to have unpleasant consequences.

If it is non-toxic, your material might be useful in heating and cooking/dinner ware: vitrified clay (as well as glass) can crack with sudden temperature changes.

I'm sure there are more valuable uses which others will offer.

  • $\begingroup$ Regarding coins, I think your caveats are a bit off. The point of testing for purity is that the material you use is rare, so that it's expensive to use in fakes. And the penalty for adulterating it is at the very least that nobody wants your money, because they can see that it's fake. If you make a coin out of a common material, you need to protect against forgery of the design, not adulteration of the metal. $\endgroup$
    – IMSoP
    Commented Dec 10, 2022 at 11:36
  • $\begingroup$ @IMSoP - I thought of that, but thought forgery of design may be low risk at that stage of development. Roman coins were defaced, but I couldn't find any evidence of actual forgery (coins long thought to be poor fakes were recently shown to be real). Forgery tended to be of documents, titles, etc. The punishment was death for slaves, seizure of property, etc., for non-slaves. People today offer rare coins that are actually forgeries. $\endgroup$ Commented Dec 10, 2022 at 12:46
  • $\begingroup$ My point was more the other way around: there's no need to caveat that the coins should be backed by something valuable, their rarity is their value. The vast majority of the population has no practical use for gold, the value of an unadulterated gold coin is that it is a known quantity of a rare material, and therefore a reliable token of value. $\endgroup$
    – IMSoP
    Commented Dec 10, 2022 at 13:21
  • $\begingroup$ @IMSoP - I thought I identified the issue of value and rarity. A 50 dollar bill is not made of expensive material; the fact that it's accepted as currency is essentially by agreement (in the US, it used to be backed by silver or gold (Fort Knox), but no longer.) $\endgroup$ Commented Dec 10, 2022 at 13:37
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    $\begingroup$ Cooking and dinnerware seem like bad ideas, since the metal container would expand significantly unless eating 100% raw food. Imagine if the pot of pasta pushed the pot of pasta sauce off the stove. Imagine if your plate shrank over the course of dinner, and some food was eventually crowded off onto the tablecloth underneath. $\endgroup$
    – Tom
    Commented Dec 10, 2022 at 23:52

If it's cheap and abundant, the Roman military will be pretty interested.

Roman pillum are javelins with a soft steel shaft, designed to bend as they hit targets, so they stick into shields and can't be removed. I can imagine a savvy roman siege engineer using this stuff as a component of ballista bolts - it would expand rapidly if it stuck in someone, making a bolt barbed with this almost impossible to remove intact. Not only can your opponent not use it to respond, but also they're more likely to die. This is great, as ballista often occupied a sort of sniper rifle role on the battlefield, used against opposing generals or higher ranked troops.

Other uses would be as a motive force for catapults - you could see a spring made of this being heated and providing a good amount of force.


Use it for sieges
if you can penetrate the wall or gate of a castle and then heat it up, you can cause said structure to crumble, making it a very effective demolition tool.



The obvious one, really.

The concept of temperature as a measurable number is almost a free gift if you have maridinium.

At some point, some Roman is going to reason that he wants either water of a particular temperature, or an exact expansion for some mechanical application.

From there, it's only a tiny jump to a practical thermometer. No fancy glassware needed. Chances are the maridinium thermometer will eventually be replaced by a mercury or alcohol thermometer, but unlike the mercury thermometer, it doesn't require someone both conceptually astute and skilled at glassware to invent it.

This has all sort of downstream consequences for ancient chemistry and medicine and engineering.

Tempering Valves

A lead or copper pipe with a maridinium plug or insert is a tempering valve. Have slaves pour hot water into a big pot with a pipe sloping down to the bath and a maridinium tempering valve, and have beautifully (by their standards) regulated baths.

Dies / crushers

Any object put into a red hot hollow maridinium vessel will be crushed or extraordinarily compacted as the maridinium cools. This is useful for fields as diverse as gold mining, metalworking, and slave discipline.

Chariot wheels and barrels

The Romans used to do their cooping by heating steel to red hot, then putting it around wet wood. When the steel cooled and contracted, it held the wood in place very strongly. With maridinium, you need only modestly heat a small section, pin it to a steel section, and the whole thing works the same. Much cheaper to heat 5% of a wheel to 50 deg C than the whole steel lot to 500 deg C. But this is only the beginning:

All manner of cheap wood/metal items

As per the chariot wheels and javelins above, maridinium gives you a cheap and easy way to attach anything to a wooden pole. From hwnd tools to structural members, wooden poles with maridinium unions are very useful!


Busts of emperors and gods can get really interesting if they grow big when warmed with water from the inside. Priests, pontiffs, etc, will love it. Surefire revenue gatherer at festivals.

As for emperors: Caligula will be so busy commissioning maridinium statues of himself, he'll have less time for making everyone else miserable.

Roman Christians won't waste their maridinium so readily on statues as the Pagans until during/after the reign of Constantine. They may take a dislike to it if it's a pagan favourite, but with all the applications above, it's hard to see them stopping using it altogether.


You can have a material with any properties you like within fiction. But this is not Metallurgy As We Know It, Jim.

You figure is about a thousand times greater than almost all metals. There are some exceptions. Plutonium changes volume when going from the alpha to the delta phase. That will happen at a specific temperature. However, at or about that temperature, both phases will be stable. The low melting point and the ability to phase change suggests that it will be pretty soft. Plutonium is not stronger than bronze, and it is hella toxic, but otherwise it gets as close as any metal does. And it would be unlikely to generate a lot of force for splitting rocks because the energy to expand has got to come from somewhere.

You could have a cubic close-packed phase which re-arranges to some lower symmetry (hexagonal or orthorhombic). This could release stored energy, but it could only do it once. And it would probably do it in a direction that you didn't want.

Memory alloys give a large shape change with temperature. They don't have the large volume change you asked for. You could realistically have a memory alloy that could be made with Roman technology. Will that do?

  • 1
    $\begingroup$ Maridinium is just something I thought up because it's fun to play around with scenarios. With that in mind, it's more fun to exaggerate that property(I think some cold maridinium will double in volume when placed in boiling water), I am aware that the rate of expansion is Highly unrealistic(I think its rate of expansion is more than AIR). But what you say are all valid points. $\endgroup$
    – KaffeeByte
    Commented Dec 10, 2022 at 21:38
  • 1
    $\begingroup$ It seems like the thrust of your answer is that OP's fictional metal is hard to believe. Generally, our remit as answerers is to accept OP's ideas (unless a frame challenge is appropriate), and run with it. $\endgroup$
    – Tom
    Commented Dec 10, 2022 at 23:59

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