Glass arrowheads

[Sam Baughn]

Originally Posted by Pursuivant

https://allthingsliberty.com/2013/05...out-of-a-body/

That link was very interesting, thank you for posting it!

[Anthony]

Originally Posted by AlexanderHowl

I think that the key utility of glass arrowhead over obsidian warheads is that they would break within the target...

In general, relative hardness is metal armor > bone > leather > skin > tissue, and if the arrowhead doesn't break on hitting the harder material it isn't likely to break on the softer material. Thus, an arrowhead that doesn't hit bone isn't particularly likely to break inside the body. Other than that, glass, obsidian, and flint are not going to be all that interestingly different in breakage behavior.

[Flyndaran]

I'm really wondering about breakage rates for misses and hitting the ground. It feels like obsidian is slightly more likely to crack. I have no evidence for my gut instinct, so I'm not married to the idea.
But I would like proof that they perform equally too.

[Anthony]

Originally Posted by Flyndaran

I'm really wondering about breakage rates for misses and hitting the ground. It feels like obsidian is slightly more likely to crack.

Pure obsidian is glass. Low quality might well have flaws and impurities not found in commercial glass, though.

[Pursuivant]

Originally Posted by Flyndaran

I'm really wondering about breakage rates for misses and hitting the ground. It feels like obsidian is slightly more likely to crack. I have no evidence for my gut instinct, so I'm not married to the idea.
But I would like proof that they perform equally too.

While I was hunting around for links for my previous post, I discovered this link:

http://www.lithiccastinglab.com/gall...turespage1.htm

So, yeah, the answer is that arrowheads made of any brittle material might fracture if they hit a hard object.

One of the advantages of a soft metal projectile point (like unalloyed copper) is that it bends or dulls rather than breaks. That means that you (or a smith) can repair it rather than having to make a whole new point.

[Flyndaran]

Originally Posted by Anthony

Pure obsidian is glass. Low quality might well have flaws and impurities not found in commercial glass, though.

I didn't mean to imply I was comparing obsidian to modern glass, but to flint and other stones.

[evileeyore]

Originally Posted by Flyndaran

I didn't mean to imply I was comparing obsidian to modern glass, but to flint and other stones.

From what I remember from learning some knapping (we didn't learn on glass, but it is basically obsidian so...)...

Obsidian is preferred to flint and chert, fired flint* and chert* is preferred to other conchoidal fracture stones (jasper*, quartz†), unfired flint/chert/quartz/jasper/etc is preferred to any other stone, any stone is preferred to wood or bone.




* 'Chert' is a broad category of stone which includes a 'quality range'. Flint is at the top, 'common' chert is in the middle, jasper (iron tainted chert) s near the bottom.

† Quartz is another huge category. I wouldn't (for GURPS sake) make any distinctions between these workable stones and flint or obsidian (or glass). I have a beautiful orange chalcedony spear head I found in the mountains. Still sharp, though I don't actually use it as a tool.

[Flyndaran]

Preferred for ease of production and construction, or for use? I know glass has uniformity of structure allowing the most predictable of knapping.

Like I wrote, it seems like obsidian would be more fragile than good stone like flint. But I don't know if that's in error, and obsidian really is just best for all sharp stone tool knapping purposes.

[evileeyore]

Originally Posted by Flyndaran

Preferred for ease of production and construction, or for use?

Yes?

The 'better' the stone the easier to knap... and it holds up better. Though some stone might be more durable (granite, diorite) they don't hold an edge for anything compared to a good crystalline fracture stone.

Like I wrote, it seems like obsidian would be more fragile than good stone like flint.

It's really not.

[malloyd]

Originally Posted by Flyndaran

Like I wrote, it seems like obsidian would be more fragile than good stone like flint. But I don't know if that's in error, and obsidian really is just best for all sharp stone tool knapping purposes.

It's worth remembering that the fact that it breaks when you hit it is the thing that *allows* you to knap a stone. One that absolutely wouldn't shatter on hitting something hard couldn't be made into a projectile point from in the first place.

But glass is also a tougher material than most people think it is. No it's not setting any tenacity records, and yes it *can* be fairly fragile if it's already scratched or cracked, but even household glass objects can survive impacts or falls that would definitely give you a serious bruise.