Crystal sword...

[Johnny1A.2]

A common trope in fantasy fiction is a sword-blade made of transparent crystal. In practical terms, what transparent material might actually serve as a viable, practical sword blade? Not necessarily practical to manufacture or economically sensible, but something that might serve as a useful sword in combat if somebody did make one?

[Refplace]

Transparent Aluminium?
Really there isnt anything. Crystals are too brittle and prone to shattering if hit wrong. Clear plastic would dull to quickly and not have enough weight.

[Celti]

Certain types of glass can be tremendously strong (stronger than steel and as light as aluminium, even). Ludicrously expensive, of course, but if you're talking high fantasy anyway, why not?

As a note, DF8: Treasure Tables took more-or-less exactly this route, with stats for "tempered glass" blades.

[scc]

Are we talking a proper sword made of gems, or are we simply talking a transparent or translucent (and maybe tinted) blade?

[mhd]

I was a bit excited a few years ago when I read news about monocrystalline turbine blades. Sadly, they weren't transparent (metal alloy) and they weren't even the big blades in front of the turbine, either...

And to match the fantasy cliche, it pretty much would have to be a single crystal, wouldn't it? With no boundaries to mess up refraction. IANAMatEng, but wouldn't that make them more unyielding, either? "Stronger than steel" is easy enough, but blades aren't exactly made for being pulled, they would need to absorb and withstand all kinds of different stresses, without shattering.

Speaking of that, the first crystal blade I remember was Ultima's "glass sword" which did shatter after a good stroke, but not before doing unprecedented 127 points of damage. That would be another approach: Have some kind of "grow your own crystal" portable lab and do some fragmentation damage.

[Anthony]

Originally Posted by Johnny1A.2

In practical terms, what transparent material might actually serve as a viable, practical sword blade?

The big problem is that it's nice if your sword blades can take a bit of punishment. Glass (both ordinary silica glass and other more exotic types) can be very sharp, but are ordinarily brittle. Various toughening methods can cut down on brittleness somewhat, but things like smart phone screens are the upper end of what we can do with glass, and they still can't take anything like the punishment a layer of metal can take. At the other end of things, you could make a knife out of a transparent plastic like acrylic, and it won't shatter, but it won't take an edge either and it's not very hard.

[Celti]

Personally, I think people put far too much emphasis on the word "crystal" when it comes to this trope. Ask somebody in the eras we're echoing, and "crystal" has little to do with geometric ordering of atoms, and everything to do with being smooth, cold, transparent, and shiny.

As for "single crystals" being more unyielding — you want your sword blades to yield. If a blade doesn't bend, it breaks. Even a super-hard blade, crystal, glass, or metal, will need to be able to deform at least somewhat so that it doesn't spiderweb with cracks and then shatter — just like your smartphone screen, and thus why so many of the new ultra-strong glasses being developed aren't just going for hardness (i.e., scratch resistance, but also the ability of a crystal sword to take and keep an edge) but for flexibility, so they don't shatter in your pocket (or when parrying a blow, or striking at armour).

[Rupert]

Originally Posted by Anthony

The big problem is that it's nice if your sword blades can take a bit of punishment. Glass (both ordinary silica glass and other more exotic types) can be very sharp, but are ordinarily brittle. Various toughening methods can cut down on brittleness somewhat, but things like smart phone screens are the upper end of what we can do with glass, and they still can't take anything like the punishment a layer of metal can take. At the other end of things, you could make a knife out of a transparent plastic like acrylic, and it won't shatter, but it won't take an edge either and it's not very hard.

FWIW, you can get an edge on plastics like acrylic or nylon, it just doesn't stay there long enough to do much. A cut or two on human skin's about it. A point lasts a bit longer.

The problem is that swords need to be able to hold an edge (requires a good bit of hardness and toughness), and be resilient (needs toughness and springiness). Plastics tend to be soft or brittle (and generally aren't super-hard), crystals and glass tends to be brittle (and hardness pretty much always means also being brittle). Even when using steel for swords, any old steel won't do, and they tend to have complex construction, and/or complex heat treating, and/or be of exotic alloys.

Knives, being shorter, are easier, for what that may be worth. Which is another thing with swords - it takes quite a big furnace by handcrafting standards to evenly heat a sword blade, and quite a big quenching bath to cool one correctly. I expect working with glass or other materials will have equally annoying requirements if you're not using some nice big modern manufacturing facility.

I expect a 'transparent' blade would be a complex laminate like modern car windshields and armoured 'glass'.

[Sam Baughn]

Would it be acceptable to mount glass (or quartz or whatever) pieces along the edge of a transparent plastic blade? They would chip and fall off, but not all of them at once. Basically a high-tech macuahuitl.

[Bruno]

Composite materials may be the only way to go here, a plastic core and a sapphire coating, perhaps?