In my world, I have ''classic'' knights but with helmets that have transparent visors which are strong enough to protect from arrows.

So which material available in medieval times could withstand an arrow shot to the face while being transparent to allow for better vision?

Or is there any such modern meterial which could be replicated with medieval technology?

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    If they had glass at all. Shutters existed for a reason. If the weather was nice shutters were open, if it was bad they were closed. Glass windows were not something one would have found in most castles. Castles were military fortifications and thus tended to be awfully spartan. – TCAT117 Oct 22 at 12:07
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    Depends on era and region. In a fortified estate in Austria, probably. In a keep on the polish frontier? Probably not. Most castles were actually pretty small affairs manned by a local landed knight or impoverished lower nobleman. Only the larger more ornate examples exist today so that's what most people's idea of a castle is. Most castles were pretty small and pretty bare bones. – TCAT117 Oct 22 at 12:39
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    Even if it could manage to survive an arrow, the first hit on the head in melee would likely send glass shards into your eyeballs even if it were a glancing blow which would otherwise not cause significant damage. – pluckedkiwi Oct 22 at 13:32
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    Have you ever tried on a medieval helm? Most of the ones I have tried, let you see surprisingly well, with only a few blind angles. – Davidmh Oct 22 at 13:53
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    @ZizyArcher angled surfaces do help against momentum. Well designed armour doesn't try to stop blows, but to deflect them when possible. – Davidmh Oct 24 at 14:07
up vote 41 down vote accepted

This is not possible, medieval glass was primitive and expensive, it was not very clear to see through and would shatter into sharp shards when struck.

We were only able to change that with the switch to plastics which involved a whole new level of technology.

The closest thing would be a wire mesh that in theory could block attacks while still allowing you to see out through it. Making the wire mesh strong enough to be useful would still be challenging though.

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    The wire mesh solution saw actual use, example on wikipedia: - although the holes in this image are quite large, helmets with finer meshes exist (just couldnt find a good picture) – Surpriser Oct 22 at 13:22
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    @Surpriser It should be obvious that this was a defense against slashing and blunt weapons - it would be exceedingly unlikely to stop an arrow, or even a thrust with a sword (possibly even a narrow-headed spear would get through holes that large). Be careful not to mistake equipment exclusively intended for tourney use as being something for a battlefield. – pluckedkiwi Oct 22 at 13:28
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    Please provide a citation for (especially because of the bolded part) "We were only able to change that with the switch to plastics which involved a whole new level of technology." My initial reaction is that the statement is not true. – Aaron Oct 22 at 18:34
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    @Aaron What part isn't true? Safety glass is composed of layers of glass and plastic. There are ways to make glass that doesn't have such sharp edges by cooling the glass down slowly but that doesn't stop it shattering, just makes the fragments less dangerous. – Tim B Oct 23 at 14:52
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    @TimB Your answer makes it sound like "not very clear to see through" was only able to change by switching to plastics. I suppose the issue was with ambiguous use of the word "that". When I read the pronoun "that", I was thinking about the clear glass from the previous sentence. – Aaron Oct 23 at 18:47

There are 2 naturally occurring materials which can - under the right circumstances - possess both the toughness and transparency to be viable: Moissanite (a.k.a. Silicon Carbide) and Corundum (a.k.a. Ruby and Sapphire). Unfortunately, this hardness makes them hard to work to a suitable thickness/shape - they at 9 and 9.5 on the Mohs scale (for comparison, Diamond is 10 and Quartz, mentioned by nzaman, is 7), and finding large enough examples to use would both be very hard and absurdly expensive.

So, handwaving time! * Jazz Hands *

If you accept the theory that the Baghdad Battery is a pre-medieval Galvanic Cell, then you open up the possibilty of creating artificial Sapphire via the Verneuil process, using Oxyhydrogen produced by electrolysis of water.

This allows you to have a heavily ahead-of-their-time alchemist-cum-jeweller who is creating artificial sheets of Sapphire, and then shaping them (with grit from previous attempts?) to form inserts that slot into the eyes slits on a metal helmet. They can also sell the offcuts to make money, since you probably only need a pair of 1" by 2" (by 0.5"?) lenses per helmet

The best you could do is quartz crystal, but that would shatter if hit directly. But then with a properly designed visor, your eye slits need not be big enough to be a feasible target for arrows, but then you wouldn't need a glass visor in the first place.

Medieval technology might not allow for direct "arrow-proof-glass", but what about periscope helmet?

Since arrows travel in approximately straight lines and cannot follow curves and bends, a helmet with an indirect visor, using mirrors, could prove useful. This idea basically comes from existing inventions like periscope glasses, periscope rifles/cameras and trench periscopes.

Proper silvered-glass mirrors did not exist yet, but simple glass mirrors did exist.

Trench Periscope from WW1

Example of a WW1 trench periscope, imagine a tiny version of this mounted on a helmet. There will not be a direct line in which an arrow can hit a knight directly in the eye.

But there are some disadvantages:

  • Worst case scenario the arrow hits in the "artificial" eyes and destroys a mirror, to avoid immobility make the helmet so that the periscope part can be detached (this adds some flexibility).
  • Obviously a knight watching through a periscope will have to deal with limited sight.
  • Depending on the precision of the periscope and the mirrors inside the hand-eye coordination could prove to be slightly more difficult.

Side note: Bascinet helmets have incredible small eye-slits, I know they are not made from glass and are far from perfect when it comes to vision, but maybe worth checking out?

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    interesting concept, but that would actually limit the vision instead of improving it, wouldn't it? But what about mirrors to see behind you can it be done with an helmet? – Gorman Oct 22 at 14:51
  • @Eries in theory yes, but not sure how practical it would turn out to be. Did you check out periscope glasses? They are quite small but extremely handy. How small would a back-mirror system turn out to be? – Rolf ツ Oct 22 at 14:54
  • I tried them once in a store, kind of confusing for a first try but it wasn't that difficult to read with them. I have no idea about the back-mirror system size but probably it wouldn't be that big I guess (?) – Gorman Oct 22 at 14:58

Polished horn is pretty rugged and flexible. Some forms are translucent to clear. Reinforce that with a mesh or something akin and you bring new meaning to a horned helm.

A bigger concern to me is getting enough air. An open face or mesh is less protective but has no such difficulty. Vigorous activity requires masses of air. If you don't account for that required exchange, people will run away from them and then counterattack when the shock troopers all have the vapours. That's just embarrassing.

(Terribly curious why you want this detail, I must confess.)

  • Was mostly a design idea actually, but wanted it to at least have the bonus of ''better vision''. – Gorman Oct 23 at 6:24
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    Welp, you can still drill in holes or use an occulted opening to provide air relatively safely. Arrows and knives don't turn corners all that well. Placing such defenses in a manner that wouldn't hamper movement or visibility would be a real trick, though. A pump of some sort could be used to push the air around the face if you want the closed helmet. – The Nate Oct 23 at 7:36

Your knights could use some sort of lacquer- or resin-based visors. While not quite as durable or thin as metal, a curved shape could be enough to repel arrow glances, and any direct hits would likely just get stuck.

These visors would likely be fairly thick, and while transparent, would probably be both dimmer and distort images a little. There would also be the problem that such a visor would accumulate damage, making seeing harder.

In contrast to other answers, I suggest that it is entirely possible to construct a visor such as you want - just not very practical.

As has been noted, medieval glass wasn't very transparent. If you can get some bright lad to come up with a technique for producing clear glass, the the solution is straightforward: make the glass thick. Enclose it in a housing of steel of even moderate thickness, and an arrow strike won't penetrate it. Put it this way: glass is nothing more than quartz, for all intents and purposes - in other words, rock. Punching a hole in a half-inch of rock is simply not something an arrow is going to do. In addition, unless the arrow strikes perpendicular to the face of the glass plate it's going to want to skip off. Modern bullet-proof materials are intended to handle bullets, and bullets have a great deal more energy and (importantly) brisance than arrows.

That doesn't mean that the result would be entirely practical. A single arrow strike in the visor would probably do enough damage to the surface to render the wearer effectively blind, and the long-term effects of being effectively blind on a battlefield would not seem to be much better than getting an arrow in the face. To handle this problem requires something like optical sapphire, and that is not in the cards for the time period you want.

roman glass

Medieval glass may not have been very transparent, but there are many examples of Roman glass that were. It would probably not be beyond the means for a medieval knight to acquire Roman glass artifacts, or pieces of them, and reuse the glass. Glassblowers could rework it with steel wire, to make a reinforced glass. It probably still wouldn't be a good idea, and would be quite heavy. But it's a starting point.

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