RogerBW's Blog

Orichalcum is a term that shows up in Plato's Critias, particularly in association with Atlantis, as a signifier of the decline of civilisation. For role-playing purposes one can do more with it.

The implications in Plato are obvious: this isn't a real metal, but just one more sign of how debased modern times are because we've lost all this ancient knowledge. In spite of this, people have tried to work out what the "real" orichalcum might have been.

The Romans mistranslated ὀρείχαλκος ("mountain copper") as aurichalcus ("gold copper"), and had an alloy which they referred to by that name; a numismatist would therefore regard "orichalcum" as the (historical) gold-coloured bronze alloy used for sesterces and dupondii.

But for role-playing purposes the mythical original has been imbued with various sorts of significance. I have GURPS to hand, so I'm drawing from there. It's generally held to be strong and light, but details are mostly lacking.

GURPS Fantasy p. 23:

"Orichalcum looks like bronze and has nearly the same density, but its DR, hit points, and structural strength are three times those of bronze."

A good density for bronze is about 8.8g/cm³. (Modern 12%-tin bronze is about 8.75, while ancient could get up to 8.9; copper is denser than tin.)

Bronze in GURPS measurements has a DR/HP of 50/58 per inch, so we'd be looking at 150/174 per inch.

Let's consider "structural strength" as being tensile strength (specifically working with yield strength, the point at which an elastic deformation stops being reversible). A modern bearing bronze has a yield strength around 140MPa; 420MPa is well within the range of steel and aluminium alloys.

GURPS Infinite Worlds p. 140 has more (for a specific alternate world):

"lighter than bronze, strong as steel"

That's rather less impressive than it sounds given that steel is lighter than bronze and strong as steel, though an easily-mined steel-equivalent would be valuable in itself to a low-tech society.

"it is also a warm-temperature superconductor"

Metallic structure isn't really conducive to this. Though if the metal were formed into a particularly rigid lattice, its structure might form convenient passages for Cooper pairs, making it a high-temperature type I superconductor. (No such is known; all the warmish-temperature superconductors are type II, allowing partial penetration by magnetic fields. So this would make it extremely valuable even without off-the-scale strength.)

"if alloyed with titanium increases its tensile strength ninefold"

Hmm. Well, titanium's yield strength is around 100-225MPa; ten times that and you're looking at the equivalent of diamond and some of the high-grade steels, though not up to Aramid fibre level. That seems almost reasonably plausible for something that acts in the ways previously described – and is fairly useful, though not worth going to major efforts to obtain.

This doesn't make good space elevator cable. Carbon nanotubes are about as strong as Or-Ti alloy (maybe half as strong in the worst case), and one fifth the density; it's the ratio of strength to density that matters.

GURPS Magic p.210 has a "retort, where a handful of orichalcum shavings melted into a pan of alchemical mercury". But I really can't see something as strong as this is meant to be being readily melted over mundane flames. Rather, it's interesting if pure orichalcum has an inconveniently high melting point, somewhere in the 3-4,000°C sort of range: that makes it harder to work with low-tech tools (everything you can do to it is effectively cold working, which will also disturb the crystalline patterns needed for superconductivity), but it has helpful implications for the material's use in demanding applications.

I seem to remember a reference somewhere to key spaceplane components being made of orichalcum (or maybe I made it up when I was running an Infinite Worlds campaign back in 2005), but I don't think this model works in that case. It may be a warm-temperature superconductor, but I bet it's not still superconducting at near-melting temperatures. If it were, that would be really useful, because you could immediately shift the heat from your wing leading edges into heat sinks in the rest of the vehicle.

But really, in order to make orichalcum a useful wonder-material at modern tech levels, it has to get more interesting. So perhaps one can readily grow single crystals of the stuff? (Zero gravity would help.) Most materials gain strength by a factor of about a thousand when grown in this way; it obviously has some single-crystal properties already, so let's give it just a factor of 100. 42GPa is a much more interesting yield strength: among other things it lets you build a superconducting space elevator, with consequent cheap solar power on Earth.