Does Obsidian Really Form the Sharpest Edge?

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But more seriously, applications for obsidian are typically scalpel tools. So it means that instead of a push stroke, it's a gliding stroke across a surface (slicing). Your setup measured sharpness of something pushing; would gliding change the parameters of the problem of sharpness?

Sharpness can also be measured on the opposite axis, dragging the edge as done if cutting a tomato. You never see a chef push a knife through a tomato. Rerun the same test with a sawing action and your results will drastically change. Measure y over x with x being a fixed distance.

Finally, someone is splitting hair on the internet!

Beyond the issue of pushing vs dragging, you may also not be producing the obsidian blades the right way: they weren't simply knapped. I do stuff with Mesoamerica (Aztec, Maya, etc) history and archeology, where obsidian was widely used for tools and weapons. I'm more informed on things like Architecture or aqueduct systems then obsidian production; but the way they did it is the prismatic blade method, which isn't simply striking off sharp shards off a starting stone, but is an actual systematic process to work a "core" piece down to produce single even blades with an insanely fine edge. This wasn't a static practice either, there were innovations in obsidian working and prismatic blade production with how the core is struck even only a few centuries prior to Spanish contact in the postclassic period, by which point the region has already been heavily urbanized with city-states and empires for thousands of years and already had a robust obsidian industry. Those innovations in blade production may have actually been what allowed Macuahuitl to pop up in the form the Aztec used them, since it could produce consistently evenly sized and shaped blades, wheras before that the types of weapons used in Mesoamerican warfare didn't tend to have evenly lined edges like that. I can't really go in more depth on this, as I said, obsidian production isn't one of the Mesoamerican topics i'm super informed on (ask me about how cities were laid out or how Aztec political systems work and then I can give you 12 paragraphs!) but yeah, it may be worth looking into prismatic blade production worked.

As someone who works with obsidian, it is extremely sharp. If cut with a piece of it, it only starts bleeding a few seconds after the initial cut. But I still continue to make arrowheads out of it.

Napping is also an ancient process used to sharpen your mind.

Obsidian can achieve a sharper edge, but doing so with any sort of consistency, or more importantly durability to handling and use, is another story.

I recall a Nat Geo article i believe about obsidian scalpels being used in surgery cause the cuts were so fine they healed much faster

As a bit of a self-appointed expert in sharpness (I'm a bit of a straight razor and honing nerd) there is a very interesting love triangle regarding sharpness. First is the thinness of the edge of course, second is the brittleness of it as you mentioned, but there is also the edge ANGLE that is critical. Basically the 'game' is to get a sharp edge that isn't too brittle by increasing the edge angle. For example, for straight razors, a 'too sharp' razor will 'fold' (or break, if the allow is particularly brittle) it's edge very quickly so is useless -- a 'too blunt' edge will mostly pull hair which makes the shape very uncomfortable. With straight razors, an edge that is too thin can be 'bevelled' by placing table (like, electrical tape) on the back of the blade and redo the edge, to increase the cutting edge angle.

Crabtree made obsidian scalpels that were used for his open-heart surgery. The trouble in these tests are multiple. As the narrator pointed out initially, the obsidian is brittle. The second error is more subtle. The "sharpness" test as employed here is simply an attempt to push the edge through the wire. That is fine for any material edge that is arguably as tough (not brittle) as the wire, but plainly isn't going to work if the edge to be tested is brittle and crushes. Also, when used as "recommended," most knives are not simply employed like a wedge. They are drawn or pushed at an angle to the surface being cut. The effective angle of the cutting edge is less than the edge angle measured perpendicular to the edge. Last, the ultimate fineness of an edge is limited by the grain structure of the material. The coarser the grain, the duller the maximum possible sharpness. Obsidian has no grain structure, nor does any other glass. This why, for extremely delicate surgeries many surgeons employ scalpels edged with glass or diamond. However, those same surgeons would not trouble with obsidian in a wood working context.

You explain everything with such care. You manage to explain even rather complicated measurement methods such as atomic force microscopy. Take pride in that, loved the video! Oh, and the visuals are also gorgeous, you have a way with cinematography.

Super cool analysis! Love to see this mix of machining and AFM 😍

It would be interesting to see some experiments of stonemasonry chisels of different materials and edge geometries and how the "cutting" action actually happens.

I love learning about edging!

Hardened tool steel, if done right, can be both harder and tougher (less brittle) then minerals of silicone dioxide. Flint actually has a granular structure (ranging from microcrystaline to cyrptopcrystaline, as formed from diatoms), which is why it's assumed to be less sharp than obsidian.

This is stunningly fascinating presentation, regardless of the subject matter. This is exactly what Tim Berners-Lee had in mind when he legged it down the patent office.

It’s crazy how many people are throwing out comments about how obsidian shouldn’t be measured by pressing down on a wire. It’s almost like he explains that exact thing and says there should be different tests for different cutting applications at the end of the video

The "point" of obsidian - weaponry. 1) Sharpness but also 2) Brittleness - the 2 most desirable features. (Which explains why copper tools were developed in N America, but didn't catch on.) Obsidian spear/arrow heads are weapons of hunting/war. In an age before beasts of burden, (all on foot! even packing out 200 lbs of meat per person!) you WANT the projectile point to do 2 things, which bring the game down faster. (You don't want it running miles away, into bogs/cliffs/inaccessible areas or found so late the meat spoils.) 1) Penetrate deep; which sharpness allows. -For maximum organ damage/ wound enlargement. (As the prey runs, each step shuffles the rock/glass pieces inside like a tumbler. Cuts more tissue/enlarging wound, severing vessels/arteries.) 2) Breaking in the wound - ensures the cutting edge stays in the prey to continue the damage. -The shaft is like a big stick, it WILL get knocked out due to the prey writhing/rolling/banging it on trees. You want a BREAK. -Non-breaking projectiles that don't penetrate far (less sharp,) can simply fall out with prey movement. The wound can close, blood can clot. Prey can flee to Timbuktu before death. Did they really want projectiles to break? Yes. Trade with others. Get your skilled knappers to tap a few times - boom, replaced. Remember - obsidian tools are "art" to us modern folks. To the ancients - disposable, replaceable, common tools. Meant for USE. "Oh it's so pretty I kinda hope it stays intact and falls out - so we lose our kill we've tracked for 9 days across a glacier and our family is at risk of starving" - said no ancient ever. :) They'd look at copper tools. Less sharp. Pain in the * to mine/smelt/craft. Soft. Really soft, yet, bendy, not brittle. Falls out of game into grass - oh who cares if we even find it? Let's go back to stone/glass!

Hey, plastic surgeon here. Obsidian scalpels are a real thing. Yes, they are sharper than any other steel edge. The obsidian scalpels are very difficult to find, but I use them on occasion. The obsidian blades are ground, and polished, during manufacturing. How? I don’t know. But they are all uniform in size, thickness, and cut through any tissue with almost zero resistance. Obsidian scalpels are actually scary to use. And that is coming from a surgeon. If you want some, let me know. Happy to send some your way.