The Ancient Art of Heat Treating Stone

Added: 2026-05-28

[00:00:16]Hello everybody, Ben Woodruff here and in today's video I'm coming to you uh I smell like campfire smoke, my hair is messed up and I'm probably a little sunburnt cuz I've been out all day working on today's video. I got most of it filmed and so now I'm going to go record the intro. So, what are we talking about today? We're talking about working with uh stone. Uh but specifically, I'm going to be demonstrating an ancient technique for heat treating stone. A lot of people do not know about this. So, let's talk about this. The art of making stone weapons and stone tools, a knife, a spear head, an arrow head, an adal dart tip, you name it. Uh that is called flintnapping. and I'm a flintnapper.

[00:00:59]This is a piece of obsidian. Obsidian is high silica. It's basically nature's glass. And if you know how to flake it and break it, you can make a razor sharp edge. It's very good to work with. Now, there are many other rocks and minerals that you can use, too. There's agots and there's flints and there's chs and there's there's all kinds of different things. Uh even within obsidian there is obsidian that has that can be kind of red and orange and brown and even rainbow blue, purple, gold sheen.

[00:01:28]There's all kinds, but some rocks fracture better than others. Obsidian is one of the easiest. So you've got a spectrum. Something like this flakes very easy, but it's more delicate. Then on the o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o opposite end of the spectrum, AGOT is very hard to flake, but it's very strong. So, you kind of want depends on what you're doing. Are you just making an arrow head? Maybe you want obsidian.

[00:01:53]If you want a knife, maybe you want to do it out of CH. Well, there are some rocks and some minerals that are so dense that you really got to do something. Here's an example. This is Kiaook CH from Oklahoma. And if you can see it, it kind of looks pink. This has been heat treated. So, this is just kind of a white stone. And if it's heat treated, then what happens is the microscopic level, it makes micro cracks and it makes it easier to flake. And it flakes in a more glass-like way. This stuff is really too tough if it is not heat treated to be able to use. This is flint. Flint can be flaked, but you notice this is pink. This has some pink and some yellows on it because this also was heat treated before. So, if you have a denser stone, again, something like banded tiger chart, we've done videos on that. If you have a denser stone, you kind of have two options. Option number one, and almost nobody knows this one, is a lot of these minerals, if on a microscopic level, if they're porous, you can soak them in water for about a month. Now, especially this is valuable if there's a lot of inclusions and a lot of little crystals in it that if you hit it's going to shatter. So what if you heat treated it, it would shatter. It would explode. So what you do in this case is you just put it in a bucket for a month and then when you take it out, it flakes much easier. But that's not going to work on something as dense as agot. So some of your other CHS and your agots, what you do instead is you heat treat them. So what you do is you dig a pit, you build a big old fire, you let it gets down to coals, bury a layer of sand, and then you put a bunch of uh pieces of flint or ch or whatever stone you want to soften, and then you put another layer of sand over that, and you build a big fire over that, and let that burn down, and then the next day, dig it out. So that's what we're going to do.

[00:03:41]We're going to give it a try. I have a wide range of stone that we're going to try it. Now, you don't want to do a whole big piece. That's too big. So, what you want to do is take a big old piece of a rough stone and hammer it down to maybe like a bif face or, you know, something narrower and layer those. So, we're going to go ahead and give this a try and we're going to do this and then hopefully tomorrow when I dig these up, they're going to be in good shape and worthy of sharing. So, the first step we got to do is we got to dig a pit. Um, it's good to go at least a foot down. Sometimes it's good to do more. Uh, it's January. The dirt is very hard, but it's been so warm that it's not frozen, fortunately. So, when you dig a nice trench, um, just go ahead and scoop it out, try to square up the edge as best you can, and then you build a fire inside. Now, the point of this fire is you're trying to make some really big longlasting coals. So, you got to build a big fire to warm up the surrounding ground as well. And then you keep building it up, building it up until you have some really hefty coals. Uh once you have that, then it's time to take a look at some of the stone we got. I've got some uh yellow quartzite here. And again, some of these I've already napped, but I've thinned them down so that they will be open to being heat treated. I got some CHS here as well.

[00:04:59]And I have several types of uh banded tiger chs, which are a bit darker, and they're they're very dense. So my hope is that we'll be able to soften them up by heat treating. So once we get these coals down after, you know, a few hours of burning and adding more and more and more, then it's time to start to bury.

[00:05:21]So we're going to take some sand and we're going to cover this up. You want hopefully at least an inch deep. You're going to cover this all with. And then we're going to go get our stone. Again, I've got I've got some agots, you know, I've got some uh nice some nice flints.

[00:05:38]I've got, again, like I said, the the Quartzsite. I've got Wondersstone.

[00:05:42]That'll be interesting to see what that does. Uh, Mort Bandit Tiger Ch. And I have some of these really neat pieces from Fremont Indian State Park. I have some cobbles that were what the Fremont in that area made their arrowheads and stone tools out of. Uh, it's very tough stuff. So, again, hoping that heat treating it is going to help it. So, [snorts] we're going to go ahead and stack these. So, we're separating them all, but we're putting them on top of that layer of sand and trying to space them out evenly.

[00:06:14]Then, uh, once I have them all in there and all spaced out, then we're going to bury them again over the top. So, we're going to bury this all with sand.

[00:06:25]And I'm going to bury it with a little bit of the dirt as well. You know, we had some leftover dirt from digging the pit. So, we're going to put a little bit of that on top. Not too much, though.

[00:06:35]You can see this dirt here on the side.

[00:06:37]That's what we're going to use. We're going to cover up a little bit of that and then build a second fire on top of that. This we're going to burn really big and really long. And we're going to let it go for hours and then eventually just let it burn itself out. And we'll just abandon it and let it go overnight and open it up in the morning and see what we got. Okay. So, now here it is the next morning. We're going to gently scrape away the fire. And the sand is right underneath. I wonder if I did not have deep enough sand. Normally, you want an inch or two deep, but it looks like it worked fine. And this one is brilliant. Look how colorful this became just from the heat treating this piece of quartzite. So, I boxed everything up.

[00:07:15]And these things were still hot to the touch. I mean, you couldn't keep holding them or it would burn you. So, I went back to the museum to try them out. This first one we're going to try. This is a piece of quartzite and amazingly it flakes beautifully. It flakes just like flintter ch and it's very soft and uh this so going to go ahead and make this into something else later on. Got a big old chunk of agot has a lot of cracks and a lot of fractures but we're going to see agot is very tough and it's definitely softened it. But again anywhere you have inclusions or cracks are going to be a problem. So something to consider, you know, maybe make smaller flakes like this, then make arrow heads. Okay, here we've got a bigger piece. This is a piece of Wonder Stone. It's a very coarse piece with hardly any silica, but it's actually still flaking off quite nice. So this is this is pretty amazing. This speaks very well. I'd rather get some high silica Wonderstone and try this out, but even the low silica worked. Okay, now here we got some oil shale. And unfortunately, it is kind of crumbling when I hit it.

[00:08:21]Is not sending a flake all the way through. So, this is a no. Apparently, uh not good with the oil shell for heat treating. Now, this is a really special piece. This is a piece of uh I call it Fremont CH. This is uh from Fremont Indian State Park. And these cobbles, the Fremont people there would take these and make these into spearheads and arrow heads. But, it's very tough stuff.

[00:08:44]I've wanted to heat treat some of this for a while. And let's take a close look at the flake cough here. And you can see just nice, perfect glassy flakes. So definitely a win on that. Now, here's some of that red quartzite. And this, oh my gosh, this stuff just flakes. It's just like butter. It's as soft as butter. It's almost as good as working obsidian. So this was a major win. Uh quartzite is very tough and hard to work, and it worked really good here.

[00:09:14]Then this is another piece of agot. I had already flaked this into like a hand knife, but again, flaking it off. These flakes are coming off nice. You still have to hit it hard cuz agot is incredibly tough, but it still worked.

[00:09:27]This definitely benefited from going through the heat treating process. So, going to want to gather up some more AGOT and try this again and just do a bigger, longer [snorts] fire and see how far we can push us with the AGOT. I hope you enjoyed um kind of seeing that whole process. It's interesting to see it from beginning to end. Took me a lot of work actually. It doesn't seem but it took hours because I was trying to build up big coals and heat the ground in the winter and then you know get the right layers of sand. So I mean it took hours of just maintaining a fire which is not a lot of work but it's a lot of mental work to try to keep because all the wood was wet and it's like okay but so but not that big of a problem. So, uh, I really need to start doing this when I go out camping because then I don't have to worry that much about maintaining it.

[00:10:17]I had to buy sand for this project. Uh, which like buying sand, there's sand out in the desert. So, I think this for people probably would be uh again, this is used for denser lithic material, things like flints and chs and agots.

[00:10:34]And it's something that is going to be uh you know very helpful to make things glassier and more nappable, easier to work, easier to make them sharp. So it's a good system. Um but I don't think people would did this regularly. I think if you just went to a quarry and you harvested a bunch of stuff, you had it on hand. Then when you had a little extra time one night, made a big old fire and did the sand and the whole thing and you just would have this on hand. So couple things I learned. So, first of all, a big old chunk, we already already knew this, but again, it's demonstrated here. A big old chunk of something is not going to get properly heat treated. It's got to be as thin as you can get it down ahead of time. So, do some rough napping to get it thin. Uh second of all, um the uh things that were on the further edge of the fire did not do as well underground.

[00:11:26]So, uh the things that were in the center got heat treated more. So, that's something again to factor in depending on how dense of a mineral you got. Um, I was surprised that the AGOT did fairly well. That big old huge chunk of AGOT definitely was softer and easier to work. Um, I found that a lot of things turn red or reddish. They get a reddish or pinkish hue, which I think is pretty cool. Um, I didn't make anything cuz I just wanted to test each one and see how it would work. The oil ch uh crumbled.

[00:11:53]It did not do well with this. And same thing with the banded tiger ch. it weakened it to a not good level. So if you're working with oil shale or tiger ch, it's best to just nap it as it is rather than actually heat treating it.

[00:12:08]But all the other things, all these other harder minerals definitely benefited from it. And that one piece of red quartzite, I mean, that thing was almost as it was like working butter. It was as glassy as obsidian. It was amazing. So, um, this is a good knowledge to have, something our ancestors all over the world did anciently, and it's largely a lost bit of technology. So, I hope you enjoyed coming along with me and uh, seeing how this works. Um, if you could, if you haven't already, if you could hit subscribe to this channel, I very much appreciate it. [music] Helps me keep the channel up and running. And always remember that life is a gift. So, never stop learning and [music] never stop exploring. We'll see you next time.