Saturday, December 7, 2013

Usable Edge Loss: Obsidian Knife Performance (slightly bloody)

Unused obsidian knife
Hi all,

Images contained in this post are a little bloody. 

It's been a little while.  As it turns out, dissertation manuscripts take up a little of one's time for other things.  I've managed to slip in some time for experiments here and there though.  I was wondering the other day  about use wear patterns and usable edge loss, specifically how do different kinds of damage occur during a single activity.  Cleaning game takes more than just slicing through meat so i was interested to see how the processes stacks different types of use wear.  Questions that came to mind were things like: What types of damage occurs throughout the process and in what order might damage compile?  Does damage come in the form of dulling only, or is there actual loss of material?  The method of butchering likely predicates the variability in tool damage, and one test can't illustrate all possibilities, but I figured it would be informative to check it out.

I procured a rabbit while out in the piney woods of East Texas for some stew, a favorite winter food for me and my brother.  I processed the rabbit from start to finish with an obsidian knife.  The red and black banded obsidian comes from the Glass Buttes source complex in Oregon (Thanks Tim D and friends!).

Ribs presented no problem

I took total usable edge for both top and bottom cutting edges before and after to see edge loss and total damage.  I used a section of dental floss and a millimeter ruler to achieve accurate measurements along the curved blade edge.  I did not use butchering techniques that would help save the integrity of the blade.  If I wanted to keep the blade sharp for as long as possible I could choose to not use it for cuts through vertebrae or the pelvis.  When it comes down to it, all one really has to to is remove the organs which can be done with one incision.  The hide can be peeled off and requires no blade.  I chose to remove the head and cut the pelvis to thoroughly clean the critter.  I consider loss to be damage incurred such that cutting through tissue is no longer possible.
The pelvis created a decent amount of edge loss


The total usable cutting edge breakdown:
initial top: 60mm
initial bottom: 65mm
resultant top: 5mm loss (8.33%)
resultant bottom: 42mm loss (64.61%)
TOTAL: 47mm of 125mm loss (37.6%)

Final edge form after use


A quick look at the patterning in the damage illustrates that I damaged the bottom (curved section) of the blade most.  This is no surprise as I used this bottom edge for cutting through bony sections.  The top was used primarily for cutting through hide while the bottom was used for cutting the rib cage, cervical vertebrae and separating the pelvis.  Usable edge loss occurred in minor amounts with ribs, rapidly during interaction with the cervical vertebrae, and less so with the pelvis.  Edge dulling occurred rapidly upon initial hide and tissue cutting and continued gradually after the initial sharp edge was lost.  The large section of step fracture damage on the bottom blade edge came last and removed signals of earlier dulling as I removed the head and separated the pelvis. 


The blade worked extremely well all said.  Different performance needs throughout the process created a compound history of edge use and damage within a single butchering event.  I was surprised at the bone cutting ability of the blade, regardless of edge damage incurred.  The blade could be used again in the current state, yet would require reliance on the top of the blade for most of the work.  While the blade worked well for all challenges presented, cutting bone, etc. a strategy of edge conservation would be a better approach.  Perhaps two tools, a sharp obsidian blade and a heavy utility edge of basalt or chert for cutting bone would combine to save the use-life of the formal tools used.


Practicing those fun channel flakes for upcoming tests

Working on overshot thinning for upcoming tests

Happy Hunting!

Thursday, October 3, 2013

Eight Years in the Making

Hi all,

Control vessel kept indoors
In carrying out the tests on this blog I can dictate some of the possibilities, sure, but overall the outcome is really about forming a deeper understanding what happened and applying new appreciations.  In an uncontrolled experiment to appreciate change in a single pottery vessel, I left a jar alone outside for the last eight years.  I like to measure the movement of charcoal, uncover, map and refit my early attempts at flintknapping, and set pottery out to die. By doing these kinds of tests I am able to see continual to change over time and observe natural forces as they reshape the contexts that supply behavioral information to archaeologists. 

 As I often come in contact with materials older than 50 generations at least, I understand that the residual of my experiments will also last much longer then my own skeleton.  About eight years ago a good friend of mine, Brad Thomson, and I spent a summer finding and using wild clay as well as firing commercial clay vessels out in the piney woods of East Texas. We had a great time that summer; I sent the biggest flake I had made to that point into my ankle bone.  Thinking back on that blood-filled boot, it wasn’t a big flake at all, and the issue was totally caused by user error.

Summer of 2005 playing with pit and kiln firing

Fall 2013. Just look at how the trees have grown!

Vertical and horizontal cracks forming in situ.

Sit tight little guy

Ceramic vessels do not break into a series of sherds that follow a normal distribution of roundness.  As shown in this test, a vessel initially breaks apart into large angular pieces.  From there, trampling by wildlife, people, movement by water and abrasion by wind move sherds towards a more rounded shape.  Also, Spalling due to fire or chemical precipitation can make sherds smaller yet still angular.

So, if one recovers an assemblage of small rounded sherds, the question must follow: were these intentionally rounded by prehistoric peoples, or are they the result of abrasion by natural processes that have also removed them from their original context.  Of course when items are out of context our job of interpreting prehistoric human behavior gets a lot harder.  See, for instance, the difference in sherd roundness between two sites that I study in Samoa.  I produced roundness measures using something called the Waddell Measure of Roundness where you divide the mean radius taken from each corner by the maximum-sized radius that can be inscribed within the sherd.  This test shows that sherds at the site of Vainu’u have seen minimal post depositional damage by water while sherds at Aoa have been significantly affected by tumbling due to water transport.  The overall significance here is that because the sherd assemblage at Aoa has become restructured by water transport, we can't really say a whole lot about pottery production over time with any confidence.  A visit to each site quickly shows differences in depositional history and erosion.  Vainu’u is flat and covered in vegetation while Aoa is on a slope and has a stream running through the area. The shapes of pottery fragments from these two sites correlate well with the visible difference in landscape topography.

 Most sherds from Aoa are rounded, while at Vainu'u they are sub angular

Intact hot rock cooking feature at Vainu'u.
This is at the base of the hill slope at Aoa

 Change over time, what a thing to watch.

Happy Hunting

Thursday, September 12, 2013

GoPro Camera on an Atlatl Dart!

Hi all!

A few friends and I were putting the gas station shootout test together when we decided to put a small GoPro video camera on an atlatl dart.  I'm really not sure if this kind of thing has been done before, I know I've never seen it.  We were all interested to see what the earth looked like onboard a flying dart so we taped the camera to the end of the weapon and set to work.  I'll go ahead and say it, this is awesome!  Take a look at this short clip that Danny Beard put together.  Danny Beard works in film and is a student at the University of Colorado at Boulder.

Danny Welch and Danny Beard with the apparatus. Photo: David Loome
You can see the compression and flex as the dart is launched.  This is one of the physical aspects that makes the atlatl so powerful.  As the dart is launched, the mass of the projectile point (or camera) at the front of the weapon forces the dart shaft to flex.  The flexed dart shaft springs forward during release and rockets through the air.  I attached the feather fletching in a way that made the dart spiral like a rifled bullet.  A spiral helps to maintain accuracy down range, just like any other spiraling projectile such as a football or a bullet.  You can see the spiraling really well on the footage.

This was a really fun side project. How cool is it to see the earth from a flying atlatl dart! Special thanks to Danny Beard and David Loome.

Happy Hunting.

Thursday, August 29, 2013

Gas Station Souvenir Shootout

Hi all!

Here we go! Look at these beauties.
The other day I was around Grants, New Mexico and ran into one of my favorite gas station novelties, gas station arrowheads!!!  Ok so you may have seen them around.  A quick look at a few attributes indicates that most flake cores were conical(ish).  By rotating the stone core, these knappers produced a series of pointed(ish) flake blanks.  Most flake platforms had the ubiquitous copper smear and pronounced bulb of percussion.  These two attributes combine to indicate removal with copper tools through direct hard hammer percussion.  Next, a quick bench grinding for shape and drill press for notches and you have a shaped stone that represents the memories of a week spent touring New Mexico.
I was (perhaps rather morbidly) curious as to how the things would actually fly and if they would go through ribs or not.  We've seen how actual hunting projectiles rain death from the sky without mercy, so let's see what tinker-toy points do.  The field school students and I bought a bunch and set off to see what these points were all about.  Of course these are not meant for hunting, they’re souvenirs, objects that make memories of vacations tangible.  On the other hand, they will be traveling at about 85 feet per second, so there is one thing going for them.
Setting up with Dave 
One problem became immediately clear; the bases of these points were actually just the un-thinned flake platform.  I had made a deal to not take a single flake off of the points so I ended up with some gigantic hafts to accommodate these things.  I gave each point the works, pine pitch glue and a fiber wrap.  A few initial thoughts as to what might happen here: Just for fun we set a hypothesis that curved points would snap at the apex of the curve.  Next we suspected that the thin hafting elements that were carved out to accept the largest point bases would snap upon impact. Finally, we picked our favorite points, placed bets and set out on our way. Hey, betting and hypothesis testing go hand in hand, right?
Hey, not too bad.

Rigged up and ready to send

The Results

To my surprise a few points actually worked ok, not great, not good…but ok.  The hafting elements really took a beating.  As we suspected, the thickness of some of the points made us have to widen the haft too much and breakage happened at impact.  They didn’t all break though. I’m working on a test that measures the tipping point for haft breakage using a diameter/internal width of haft measurement.  Things are coming along on that but I need more darts.

The two impact marks from a curved point snapping

Most of the points bounced off of the carcass with minimal damage to the target.  A few made little wounds then snapped.  The curved points made some interesting damage patterns.  First, unlike our hypothesis, breakage on the curved points appeared to occur at the junction of the haft.  A slow motion camera would be awesome for looking at that!  A pattern seems to exist that upon impact the curved tip snaps and makes an initial wound with a secondary impact occurring as the hafted fragment hits.  Neither of the wounds were a big deal. 

dull wound edges made by gas station points

The bench-ground edges of the points mashed their way through the soft tissue between ribs and did more scraping than cutting within the wound path.  The wounds are rounded about the periphery of the opening in comparison to true hunting projectile that make a rotating lenticular pattern.  It makes sense that these points do not penetrate far and have dull wound paths.  Sharp points allow the momentum of a dart to continue through further than dull points that create more friction.

Overall it pays to outfit projectile points with sharp edges too, not just sharp ends. There’s probably a joke in there somewhere about staying sharp and edgy.

Happy Hunting.
These hafts are too thin

...what a surprise
clean lenticuar wound from a bifacial projectile point 

there was no way this rig was going to work, destined to fail

Bad bruise, yes. Dead? No

Tuesday, August 27, 2013

Coming Unglued: Testing the Efficiency of Hafting Techniques

Hi all and welcome back!

I just finished about three months in the field where writing up blog posts and firing them off on the interwebs was a bit of a challenge.  But! I was able to have some fun setting up tests and helping out on some really great archaeology.

I have been looking around in the literature from cave sites to see examples of different ways Archaic points were fixed to atlatl darts.  The four main ways evident are:

1) jammed into a hollowed out socket

2) set with an organic resin of one sort or another (even fish head glue in California, see Gifford and Klimek 1939:82)

3) wrapped with animal sinew that dries and tightens

4) a combination of hardened mastic with a wrap of animal sinew or fiber.

Tapered haft and pine pitch glue
           Each of these attachment methods no doubt comes with a specific suite of costs and benefits, some of which naturally overlap with other hafting techniques.  An example of overlapping benefits is that all techniques allow an armed weapon to be projected towards a target.  Unique characteristics, among others, include the cost in time and resources of collecting and processing raw materials.  For the hunter, each method creates a different working relationship between the stone point and wooden shaft.  Imagine not wanting the point to stay attached to the foreshaft after a target is hit.  Perhaps there is a benefit in having the foreshaft detach from the projectile.  If so, a socketed or glued point may actually be the best approach.  Think of close successive shots on game in corrals like we see in the Great Basin.  Perhaps in brushy areas where points get hung up on vegetation, and game may run once hit, a barbed point with pine glue and sinew may be a good way to keep weapons in operating order after a miss or to ensure secure hits that may be easily tracked. 

For an interesting discussion of hafting techniques and the decision between bow and atlatl you’ll enjoy Margaret Nelson’s analysis of food selection and hunting choices used by the Mimbres Valley Salado (Nelson 1986)
The Test

The possibility that tightly fixed projectiles might not always be optimal led
me to arm a few darts and check out what the suite of the cost/benefit differences might be with different hafting approaches.  For this test I chose to observe differences in point loss, point breakage and shaft damage between three types of hafting: 1) pine pitch glue 2) pine pitch with goat sinew 3) pine pitch glue with a fiber wrap.  Additionally, I chose to use both conical socketed and carved-post foreshaft types to check out any benefits of one type over another.  Finally, for a few darts I attached the point directly to the mainshaft of the dart with no foreshaft and no reinforcement wrapping.  Hafting element damage as regulated by attachment method is one thing that we rarely see archaeologically. Hopefully this test will illustrate some functional benefits of each technological choice.

Pine pitch, fiber wrap and carved-post foreshaft
Fiber reinforced mainshaft with pine pitch

A Quick Word…

The test provided a few interesting observations that apply to the archaeology of technological choice and environment.  A larger sample with a consistent shot placement machine would allow observation of strict physical differences in point breakage and haft failure.  But isn’t there a human constant to the equation? So as not to brand the results of exploratory tests with strict physical/functional/temporal explanations, we must consider:

1) Stone tool manufacture and use was an active and transformable adaptive strategy. 

2) Manufacture and use fluctuated as dynamic cultural subsystems, which were conditioned by technological choices and maintained or transformed through cultural transmission processes (see Rickless and Cox 1993 for dynamic cultural subsystems).

3) Variability in technological organization exists spatially and temporally, between and within lithic assemblages, as a result of culturally transmitted production and use practices tailored to subsistence resources.

Allowing variable shot placement in an exploratory study like this is one way to see a wider range of possible outcomes.  Strict questions necessitate tight controls.  My reconnaissance, on the other hand, initially welcomed uncontrolled test environments. 

The Results…

            A few patterns came to light.  First and foremost, the fact was reinforced that some type of binding is optimal just below the hafted projectile and also on the mainshaft where the foreshaft is seated.  A fiber or sinew wrap prevents splitting of the shaft upon impact.  Without binding, the base of the seated point turns into a reverse wood splitter and tries to shred the entire assembly.  Using hardwood shafts with an irregular grain may reduce the need for a fiber or sinew wrap. 

This didn't work out all that well.  A fiber or sinew wrap makes all the difference


Second, nothing too illuminating, but when creating a new point for an old haft, try to thin the point out and test how it sits in the haft prior to final notching.  Late flaking passes to thin out the base after notches have already weakened the projectile may lead to unnecessary point breakage.  There are a few tricks for post-notch basal thinning out there though.
            Next, pine pitch alone is far faster to rearm as opposed to pitch and sinew.  Sinew offers superior staying power and breaks free much less often but requires at least thirty minutes to set properly.  Pine pitch alone was ready to launch after five minutes. A healthy lump of pine pitch would offer minimal preparation cost with favorable outcomes in instances of close successive shots where breakage is likely to occur and projectiles are plentiful.  I lost the majority of points this way; they’re out on the shooting range somewhere. 
            A wad of pine pitch that has been shaped to a low profile and wrapped with sinew is the best combination for not losing points.  This is no huge surprise.  Even when the entire haft broke there was still a line attached to the projectile that I could follow and recover. The goat sinew worked out ok, the segment that I used was a little greasy and didn’t offer the strength that deer backstrap sinew gives. 

Broken foreshaft post, at least the fiber wrap did its job

 The Quartzite point attached with pine pitch glue and fiber wrapping turned out to be an absolute workhorse.  While the raw material took more effort to create due to its tough structural nature, the completed weapon powered through brush and finally broke against a telephone pole (the point was fine but the haft slot broke). Darts with fiber or sinew wraps around the projectile point appear to break the actual hafting element more often than glued points.  If you do not have an abundance of hardwood for foreshafts, you may want to consider gluing the points rather than gluing and wrapping to save wood.  Alternatively you could re-groove a new slot each time...but that takes forever on hardened wood.  I wonder how many discarded hafting fragments have been identified in the archaeological record? probably not too many.  A spatial patterning map for fragment types would be a fun thing to look at though.


Breakage pattern of a haft with binding
point loss and haft damage with no sinew
Perhaps obsidian points with pine pitch alone would be the most efficient use of time in instances where points are plentiful, prey is close by or contained and multiple impacts may require you to constantly glue points to foreshafts.  Longer shots in brushy areas likely come with a higher risk of missed shots and entanglement.  Robust lithic materials with socketed foreshafts and sinew-wrapped pine pitch glue hafts appear to offer an efficient use of one’s extra “gearing up” time in unknown or difficult hunting environments.  As to the carved-post type foreshaft, I’m never trying it again.  Upon breakage the foreshaft post plugs the mainshaft and prevents rapid removal and reuse.  I tried it and it’s a no go for me.                      

One last thing, of four points tested with glue alone, all became detached after the first missed shot.  None of them broke. Instead they flew off end over end to be recovered later.  Alternatively, the sinew wrapped points suffered breakage as a result of reduced ability to break free of the haft upon impact with brush and soil.  There may be something to that; I’ll have to check later.  Could it be that weaker hafting has a proper place in the halls of atlatl glory? 

Reworked obsidian point with sinew

This was the resultant break against a rack of ribs

Thick points with plenty of pine pitch destroy bone and tissue no matter what

My personal favorite of the day: fine-grained quartzite with the works
Happy Hunting!

 References Cited

Gifford, Edward W., and Stanislaus Klimek
            1939    Culture Element Distributions II: Yana. University of California Publications in American Archaeology and Ethnology Vol. 1(1): 1-222 

Nelson, Margaret C.
            1984    Chipped Stone Analysis: Food Selection and Hunting Behavior.  In Short-Term Sedentism  in the American Soutwest: The Mimbres Valley Salado.  By Ben A. Nelson and Steven A. LeBlanc, pp. 141-176. Maxwell Museum of Anthropology and the University of New Mexico Press.

Ricklis, Robert A. and Kim A. Cox
         1993  Examining Lithic Technological Organization as a Dynamic Cultural Subsystem: The Advantages of an Explicitly Spatial Approach. American Antiquity, Vol. 58, No. 3, pp. 444-461

Thursday, June 27, 2013

Ground Stone Workshop

Hi all,

The world of stone tools is of course so much larger than flaked projectile points.  Ground stone artifacts played a major role in processing food, making other tools, jewelry, house construction, warfare and a myriad of other uses.  The other day we were lucky enough to have Jenny Adams come out to the field school to give a ground stone artifact workshop.  Jenny is the author of “Ground stone Analysis: A Technological Approach”.  Her exceptional book details the use of stone tools that were shaped by grinding and pecking and illustrates the methods that archaeologists use to collect meaningful information about these kinds of items.  Here are a few highlights from the workshop!
Grinding corn with a mano (hand held grinder) and metate (large U-shaped basin) proved to be quite the task and showed how much effort really went in to creating a meal for hungry families.  These formal items are often found within prehistoric room blocks associated with mealing bins where corn flour was produced and collected.  

The groundstone axes and war clubs were amazing.  The effort to create these tools is astounding to think of.  If it took me an hour to cut through an atlatl blank with a stone saw, imagine the effort expended on the creation of these items!  The size of the artifacts were a little unsettling as well; I would not like to have this coming at me, nope, no thanks.

Stone drills were often used to hollow out pumice or other vesicular volcanic stone to create smoking pipes.  The stone drills performed fantastically and made relatively (as in it still takes a while) quick work of stone pipe bowls. 

The use of tabular stones for grinding small holes on shell for ornamentation was an interesting endeavor that illustrated the time investment locked up in a single necklace. 

The groundstone implement for straightening arrow shafts was also pretty fantastic to see in action.  I would like to have one of these little gadgets for sure.  By passing the arrow shaft back and forth the shaft becomes smoother and straighter, all the better for zipping though the air!

thanks for coming out Jenny!!