One day, Kesser the Curious, a 13th-level wizard with a 22 Intelligence score, pondered the question: can a rust monster really dissolve a cube of metal ten feet on a side with a touch?
For the advancement of arcane knowledge, Kesser obtained one rust monster and restrained it in a sturdy wooden cage. (Rust monsters aren’t very strong and their feeble bites—1d3—won’t even penetrate the hardness of wood. Even on a critical hit, which you typically can’t get on an object, it would only do one point of damage.)
Having obtained the rust monster, Kesser proceeded to cast wall of iron many times over the course of ten days until he had a ten-by-ten-by-ten-foot cube of iron. With each casting he made a ten foot by ten foot by three inch slab, cast shrink item to shrink it down to a square metal plate 7½ inches on a side and 3⁄16 of an inch thick. He could cast three wall of iron spells daily—four if he used his 7th-level spell slot, which he did—and shrink each down (for up to 13 days) to lay it down flat safely and stack them, until he had cast the spell forty times over ten days and stacked it all into a neat cube, ten feet on a side, which he then simply dubbed “The Cube”.
Satisfied, Kesser then released the slavering rust monster, which made a beeline for The Cube.
Now for some serious math.
A cube of iron ten feet on a side has 1,000 cubic feet of iron. The specific gravity of iron is 7.85, which means a cubic centimeter of iron weighs 7.85 grams. There are 28316.8 cubic centimeters in a cubic foot, so there are 28,316,800 cubic centimeters in The Cube. Multiplying that product by 7.85 yields 222,286,880 grams, or 222,286 kilograms, or a bit over 222 metric tons. (A metric ton is 1000 kilograms or about 2,200 pounds, 10% more than the short ton at 2,000 pounds.)
That’s…a lot of iron.
What Kesser did not know—or failed to take into account—is that the oxidation of iron is an exothermic reaction. In short, iron rusting releases heat. Normally, rusting occurs at a fairly slow rate, and this heat dissipates without notice.
How much heat?
Well, without going into too much extra math, 50 grams of iron rusting releases 409.2 kilojoules—that’s 409,200 joules—of heat. A joule is the amount of energy needed to move one kilogram (2.2 pounds) one meter (a bit over a yard). While that sounds like a lot, 50 grams is just 1.7637 ounces. That can’t be all that much, can it?
Well, not if it’s done over time, no.
But The Cube contains 222,286,880 grams of iron. Divide that by 50 and multiply the result by 409,200 and you get 1,819,195,825,920 joules.
All released in less than a six second round.
But that’s a number big enough to be meaningless. We need context. What should be used as a comparison? Well, the energy released by the detonation of a ton of TNT is commonly rated at 4.184 gigajoules. That’s 4,184,000,000 joules. So if we divide that into that…hmmm…
Kesser, the rust monster, and a good part of the countryside is immediately vaporized by a blast equal to 434.8 tons of dynamite exploding. The bomb that destroyed Hiroshima was the equivalent of about 15,000 tons, so this isn’t quite on the scale of a nuclear warhead, but still…
Kesser was highly intelligent but Wisdom was his dump stat.
Worse yet, the rust special attack on a rust monster is an extraordinary ability, which means it is supposedly nonmagical (Ha! Ri‑i‑ight…), so even an antimagic field wouldn’t prevent the blast.
Ahem. Rust monsters do not exist in my games. So don’t even think about it.
And be damn careful with the rusting grasp spell. Or, you know what, never mind. That’s magic; the spell vents the exothermic reaction safely to another empty plane of existence or something. Druids aren’t gonna blow up the landscape with a lousy 4th-level spell.
This has been another episode…of Experiments in Wizardry.