Q&A: Diamond Swords

Hello! I was wondering if a sword with a diamond blade be of any use. I know that diamonds are often used for cutting things and are (to my knowledge) one of the hardest materials on Earth. Note: This is a fantasy story and a few people have the ability to manipulate diamonds like other metals so getting it the shape wouldn’t be a problem and there aren’t enough people with this ability to make it a weakness on the battlefield. Thank you!

I honestly thought I answered this ages ago, but apparently I never wrote the post.

Diamonds are usually presented as the hardest substance, but this is a little misleading.  In mineralogy, “hardness,” is not the same thing as “toughness.” Hardness is used to evaluate how well a substance resists scratching. In this regard, Diamonds are amazingly hard, and it’s almost impossible to scratch the surface. This also makes it difficult to selectively cut a diamond. They are not particularly tough, however. Toughness is the evaluation of how resistant a material is to fracturing.

So, your diamond sword will never be scratched; that’s kinda cool. However, your diamond sword will crack and shatter if you parry an incoming strike with a steel blade. Now, those shards won’t pick up a scratch but you’d be hard pressed to use the remains as a sword.

To be fair, I’m not certain if this will happen on the first blow, or if it’ll take a few hits before it breaks. I’m also fairly certain it could break after stabbing someone if the blade was torqued incorrectly on the way in or out. Dropping your diamond sword is also a bad idea, for the same reasons.

There’s probably some larger metaphor here for the entire idea of creating invincible forces, but not being able to shore up the actual system that supports them, or just the idea of having one unassailable defense, but nothing shoring it up, allowing your enemy to simply skirt around.

Okay, that’s the part where this doesn’t work. So, what does?

You could, potentially, use some kind of synthetic diamond coating over a blade. I may have a synthetic diamond knife sharpener around here somewhere, come to think of it.

You could have a blade where the primary core is steel (or some other material), but the blade itself is a thin diamond inset. For what it’s worth, there is some merit to this design, as the concept is somewhat similar to the real macuahuitl, from Mesoamerican civilizations. At that point it might not even matter if individual stones shatter in combat as they might be replaceable. It might also be possible to “coat” a steel core in diamond and use that. It would still crack, and eventually shatter, but it would probably see some use before that happened.

Steel weapons with carbon nanotube structures do exhibit extraordinary durability. Though those aren’t how we usually think about diamonds. This probably includes Damascus steel, and does include some other superalloys.

If your setting had the capacity to make diamond weapons, then you could reasonably see those as ceremonial pieces, or given as gifts. You might be able to come up with some other uses, such as medical tools. But, ultimately, the applications are severely limited.

However, if there’s magic in your fantasy setting with the ability to overcome the detriments of brought on by real diamonds then feel free to go hog wild.


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