Sharpness of the medieval swords

INTRODUCTION

From historical point of view: the sword was designed to hit shield, helmet, chainmail, fresh and bone... so - not to cut the paper or plastic bottles.
So, the historical sharpness wasn`t this kind as we imagine today - they were sharp, but also had a strong edges, sharpened at an angle so that they do not become too delicate.
In fact, we could end that article here, but the matter of sharpness returns and not everything is clear here.
This clearly has to do with how we define what is sharp today, more or less.
The term 'cutting sharpness' is what we TODAY use to have for cutting SOFT targets, and that would means 'knife`s cross-section on the edge' to cut them well.
But what does 'cut' actually mean when talking about a blade?
Let's try to distinguish some basic things at the beginning and compare the three most popular types of blades:
- knife edge is very thin and designed for moving on/through something to cut this to pieces, not to hit in something tough.
- ax edge is also sharp, but is designed to hit the target and split/chip it. The ax blade sticks like a wedge on impact perpendicular to the target. The ax is not exposed to bends and stresses because its strength is ensured by the thickness of the material.
- sword blade in some ways has the features of both of the above blades, but it is also unique.
All these qualities are manifested in what the blade is intended for.
So, let's talk about swords below.

SWORD SHARPNESS: Medieval and present day

We all have a lot of fun cutting things like fruits, plastic bottles, etc, there's nothing stupid about it and I have nothing against it, but these are not sword tests, only games in the yard and sometimes even a good practice. Safe, professional competitions in which we test our cutting techniques are another beautiful tribute to the ancient weapon: the sword.

But is that a criterion for whether a sword is good or bad judging only by its sharpness in such tests? Well, it is not and even shouldn't be.
You can even sharpen a piece of sheet metal or a piece of car body and it will cut paper or plastic if the edge is thin and smooth as a razor. The blade of the sword has its own purpose.
Yes, the sword was and should have been sharp enough for its purpose. There are other specially designed tools for shaving or making paper cutouts.

I like when the sword is sharp. I know then that it will cut whatever stands in its way, when it comes to action for which it was designed. As long as a piece of paper or a plastic bottle are not our opponent.

However, today sharp swords are no longer used on battlefields...

Also, what's the point of cutting meat, for example, to test a sword? You might as well do this with a kitchen knife, carpenter's ax or machete that aren't designed for combat.

The problem is we're using the wrong tests. To test the effectiveness of the sword and not to hurt anyone, you should put the meat with a bone in the gambeson sleeve, put on chain mail or plate armor and hang such an object loosely. It will be quite close to objects that a sword blade may encounter on the battlefield or in a duel ages ago. Such an item will also be, for example, a shield or a helmet, because the edge of the sword must be adapted to withstand such blows or thrusts in the best condition.

So that's why it can't be a thin, delicate edge, but a strong and thickened blade. Hints are, for example, Passau blades from 14th century. The designers wanted to strengthen the edges of the blade while maintaining the remaining parameters of the weapon, its functionality, elasticity and aguility. The edge was not thin but thick.

But does that mean the swords were blunt? Of course they were sharp! Sharp and durable at the same time. Sharpness is not only about cutting ability, but also about being able to survive when you hit an armor, other blade or a shield. And that is why swords are designed differently from, for example, a razor or a kitchen knife, not intended for use in battle. It`s about the cross-sections and angle of sharpening what makes them significantly different. The differences are significant but often incomprehensible to the modern user.

Let's take an example: we have a sword, slightly sharpened, but not very sharp. We beat it into a melon and easily cut it in half. There is even no resistance. This is how the geometry of the blade works when meets the structure of the melon. But with such a blade we will not cut the paper across or shave. These things will be too delicate for the sword edge! The structure of the thin paper is strong, completely different from the fruit. A plastic bottle has a smooth surface so only a very thin, sharp edge will enter it on impact.
Because slicing and hitting are two different things. Cutting is a sliding movement along the edge, but we hit point-wise. In fact, most sword cuts are more like blows! The contact point is very small there, there are enormous forces at the point of contact. Depending on the moment in the fight, these are cuts, hits, parrying and thrusts. Not a controlled pulling on the edge of the sheet of paper, though sometimes it also happens when there is an opportunity.
However, as we know, even a piece of paper or cardboard can cut well through our skin if we pull it quickly. Although the paper is not steel, it just has a thin edge. Anything with a thin and long edge can cut, e.g. a piano string or even a hair.
This is exactly how important the structure of the object we are cutting is. We will cut the pancake with a blunt plastic knife, but we will not cut the paper with something like that.

This is why such a tests in relation to the sword is not reliable. A sword may be sharp enough to be effective in combat and perform its function, but at the same time it may not cut through the paper. Maybe that's why scissors were invented 3000 years ago?

What exactly is the degree of sharpness and does it matter for the quality of the sword? Of course, the degree of sharpness is important for a tool such as a razor, because it is related to its function. This is also important in the case of a kitchen knife, which is also related to the function. These tools just have to be very sharp to work. Well, it's about what a given tool is for, then the blade cross-section and the sharpening angle are designed differently. Some tools and knives, for example, are sharpened only on one side. The swords were sharpened on both sides.

The edge sharpening angle depends primarily on the variable geometry of the blade, type and cross-sections. You should sharpen the edges, not the whole flats, of course. This is also a hint that shows the geometry of the edge.

The extent to which we can sharpen the edge of the steel is also related to the quality of the steel, its composition, hardening and the general characteristics of the material in the final stage of the making process.

So it will always be a compromise, because the harder the material, the more we can sharpen it and it will keep that sharpness longer. However, it will be more fragile, e.g. on impact. The sword has a long blade that is susceptible to vibration and shock. Therefore, it cannot be fragile but hard, flexible and durable. This is a compromise between hardness and flexibility that we find in good swords.
However, the file, as a tool, does not have to have a sharp edge, so it can be very hard and fragile. Also small chisels, e.g. for engraving, are very hard and sharp, but they are only used with a short, controlled movement for artistic work.

REFERENCE TO JAPANESE SWORDS

The characteristic and specific cross-section of the sword's blade in various types, reflects also the functions of the sword. Let's look at Japanese swords for a momment. The cross-section of the katana it clearly has two planes: the plane of the blade angle and the plane of the flate, the upper zone.

And the cross-section of the European sword is different, the angle is different, the cross-section is different, the specificity of steel and hardening are different. This is simply due to the widespread use of protective armor in medieval Europe (chain mail and then plate armor). Therefore, finer, thinner edges with high sharpness were not preferable, which was in turn desirable in Japan, where the armor was made of leather, laca, fabric or rice cardboard. The edge departure angle will therefore always be different, similar to, for example, an ax - to hit and chop rather than to cut with a sliding motion. The consequence of this are, as you know, also the shape of the blade (straight vs curves) and fighting techniques. So it's hard to make a historical cross-section of a European sword in such a way that it cuts some soft objects and stay sharp, like a Japanese katana with a thinner, flat blade, hardened yakiba area in the hamon zone.
It is also difficult to use stones for sharpening the medieval sword`s edges, the stones are flat and intended for flat surfaces, like a katana. Here we have a slightly oval edge (apple stone cross-section). Therefore, for sharpening European swords mainly stone wheels were used, placed on a stand, with different hardness surfaces (just like we currently use different gradations). Historically, everything is fine. However, from the perspective of someone used to Japanese swords, or simply testing on soft objects, it will just be a less sharp blade for sure, because an angle. But - you can try to smooth the edge itself to slightly improve the sharpness. However, this may not be effective for long. Katana usually has a yakiba area hardened around 55-60HRC and the mune back around 40-49, which of course gives flexibility, also compensated for by thickness. This is the famous selective hardening that produces a visible hamon.
The hardness of European swords has been average and constant since the end of the 10th century, due to the spread of steel smelting in blast furnaces on a massive scale. In Japan and in the Middle East, steel had to be mixed and combined with each other, one of the reasons why the best part of the blade was the cutting edge, which was thermally tempered and made of the best steel.
So as you can see, such inventions were developed which worked best in given conditions, environment, availability of materials, etc.

CONCLUSIONS

Has this matter been cleared? Certainly not. Certainly, many people who use or collect swords today have their own opinion and preferences, their own needs related to the degree of sharpening of the cutting edge of the blade. However, nowadays we do not use the sword directly as a weapon on the battlefield, and it is always the main criterion for the functionality of a given weapon. So if the sword is used today as a collector's item or as a replica for a historical reconstruction, the criteria have also changed. Assessment criteria are based on demand and expectations.

So is demanding a very sharp edge on a sword blade the right approach today?

If someone is going to use a sword in a target cutting competition, intended for this purpose, e.g. wet tatami mats, it will require a very sharp sword, preferably designed and hardened from scratch, bearing in mind its function: professional cutting competition. This is the case, for example, in Japan, where such competitions have been held for many years and they use swords with a thinner cross-section and a much wider blade than the old combat swords. Why? Since these competitions are considered part of the tradition there, they are taken very seriously with the use of special swords for best results.

The degree of sharpness required for any object or tool depends on what it is designed for. The degree of sharpening of the ax will be sufficient for chopping wood, but not for shaving. If we take a shaving tool, we will check that it has the correct sharpness by a shaving test. If we take a paper cutting tool (scissors or wallpaper knife), then we will also check it by cutting a sheet of paper, not chopping the wood. Of course, we can sharpen an ax or a sword to cut thin paper, but this will not be a determinant of evaluating this tool because it was designed for different purposes.

Interesting articles online:
https://blog.lostartpress.com/2019/01/16/sharp-edges-cut-out-profanity/
https://www.hertzmann.com/articles/2013/edges/
https://medievallondon.ace.fordham.edu/exhibits/show/medieval-london-objects2/whetstone