Primitive Archer
Main Discussion Area => Flintknapping => Topic started by: iowabow on July 11, 2013, 11:07:06 am
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The fire was started yesterday at 11:30. I graphed the rate of climb and and made a couple videos that cover the mechanics of the process and drew a couple drawings to illustrate what I believe is happening. I learned a lot from this process I hope you find it as intresting as I did. (videos should be up later today.
Pictured below is my sand pit with chert below 2" of sand. The fire was started in a secondary pit and then transferred. Videos will explain the rest. (video to be add later today)
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This picture is typical of the fire structure I used during most of the firing. The pit is cooling still so the will be no peeking till it is cool. Results will be posted on friday.
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Sounds like a topic that has not been thoroughly explored, yet many have done in various ways. I hope you got enough heat. Looking forward to hearing the results.
It rained here in Arkansas last night and that got me thinking just now about how many of the old ones went to the trouble of doing this process only to have cold rain soak down into the hot rocks and crack them. In accheological deposits, we find plenty of heat cracked rock, though much of it is not knapping material. Maybe they could cover their pits with a skin or something and save the batch?
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Sounds like a topic that has not been thoroughly explored, yet many have done in various ways. I hope you got enough heat. Looking forward to hearing the results.
It rained here in Arkansas last night and that got me thinking just now about how many of the old ones went to the trouble of doing this process only to have cold rain soak down into the hot rocks and crack them. In archaeological deposits, we find plenty of heat cracked rock, though much of it is not knapping material. Maybe they could cover their pits with a skin or something and save the batch?
Great question about the pit fire and rain. Last year I wrote a post about pit firing native pottery and a storm came up. I covered the fire with dirt and old ash then covered it with very large leaves that were growing in the area. It rained but did not harm the ceramics if I remember correctly.
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The fire continued for hours inside
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The temp remained high. In the pottery firing the pyrometer was located differently that with the chert project but as you see the inside temp remains very high.
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This was a picture of that storm.
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It survived the edge of the storm but not sure it would have if the eye pasted over me. Yes a deer hide would have been a possibility. Thats a good idea I will remember that for sure.
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Good Stuff John! I'll have to find a high-speed connection soon to watch all these vids. ;) dpg
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I kinda feel like a kid on Christmas eve waiting to see what comes out! I appreciate you doing this John. This is something I really wanted to know more about. Josh
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Derick I am loading them as I am typing. My videos are shaky but the verbal is the most important. I had Isaac do one of them and when you watch it you might feel like your on a boat lol. I hope people get the general idea anyway. I am going to break down and buy a nice camera at some point and stop using my phone.
I was tell you earlier that the fire was still going and when I left the house it was still at 450 degrees so I am shocked at the rate of drop being so slow. I have done many pitfires with pottery and they seemed to have dropped faster, must have something to do with the sand. So the hold time at one temp is unbelievable
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Here are the videos I made yesterday and today. I will wait till tomorrow for the pit to cool before removing flakes from the pit. I dont know if it worked but I did learn a lot in the process. (maybe they are all broken because of the fast ramp at the beginning...well we will see!). This is an ABO like process but can't really call it that unless it was done blind (without the pyrometer). Next time I will work the fire and have another person record the data and see if it works out the same. In this way we can compare the results that I think I am getting with real data from the pyrometer.
Video #1 http://youtu.be/c_ealcGbxE8 (http://youtu.be/c_ealcGbxE8)
Video #2 http://youtu.be/niwvZh19Y7Y (http://youtu.be/niwvZh19Y7Y)
video #3 http://youtu.be/JcVO_hvsERs (http://youtu.be/JcVO_hvsERs)
video #4 http://youtu.be/R8kboAVe6Jg (http://youtu.be/R8kboAVe6Jg)
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John, Question, why would you not build fire on the covered spalls an have slow ramp up, an seems more effcient to only heat up one place an not worry about moving hot coals? Bob
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My first thought was to build the secondary fire then transfer the coals so that the bed would evenly heat at the same time. Additionally I thought that the smaller sized wood would burn much higher and build heat to quickly. When I transferred the fire I did it in a thin and even way but as I stated the pyrometer was reading backwards because the connections were switched. So I build the fire up to large in the beginning based on the false data from the pyrometer (should have stayed with my gut). I do see your point but I wanted the entire surface to rise rather than the center where the probe was located. This is my first attempt and will redo this again in a couple days blind so to speak. I am looking for an assistance to record data while I work the fire carefully and slowly and then compare results. It may be that the fire needs to start as you described just not sure yet which way to go because I have not see or tried the results.
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Here are the videos I made yesterday and today. I will wait till tomorrow for the pit to cool before removing flakes from the pit. I dont know if it worked but I did learn a lot in the process. (maybe they are all broken because of the fast ramp at the beginning...well we will see!). This is an ABO like process but can't really call it that unless it was done blind (without the pyrometer). Next time I will work the fire and have another person record the data and see if it works out the same. In this way we can compare the results that I think I am getting with real data from the pyrometer.
Video #1 http://youtu.be/c_ealcGbxE8 (http://youtu.be/c_ealcGbxE8)
Video #2 http://youtu.be/niwvZh19Y7Y (http://youtu.be/niwvZh19Y7Y)
video #3 http://youtu.be/JcVO_hvsERs (http://youtu.be/JcVO_hvsERs)
video #4 http://youtu.be/R8kboAVe6Jg (http://youtu.be/R8kboAVe6Jg)
John,
This is exactly what I needed to find! One of my posts has some picts of some stone I have found and I think needs heat treated.
The yellowish stone is a type of chert? it is in your first video. I have found a bit of that thinking its a quartz that is stained w iron.
Thanks for the vids,
Greg
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Quartz can fool ya sometimes and look like burlington. On more than one rock hunt I picked up quartz thinking it was high grade stuff...now I can spot it a little better.
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Thanks for the videos and photos John. In response to the comment below: I collected some projectile points in the 1960's-70's that looked like quartz to me at the time. Upon further inspection years later, I realized that some were made out of a heat treated white translucent chert from the Savannah River area. Some chert can fool you sometimes and look like quartz. Rick B
"Quartz can fool ya sometimes and look like burlington."
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What I am about to tell you is odd and raises even more question. My pit is now reading 515 which means it rose 85 degrees since 5:30am and it is 4:30pm.
So the graph would look like a wave and be functioning unlike a kiln. This is only if the fire was left alone the way I fired my pit. The way I have it figured the fire created unburnt charcoal that is now recieving oxygen and burning hotter than the logs would burn because the charcoal is now very pure burning and very hot this heat is now closer to the chert at this point. So unless you remove all of the fuel after firing this process might repeat in another experiment. So this would suggest that primitive chert firing was fired differently than how the modern knapper heat treats chert today and that includes me. Does this make a difference? I dont have a clue but if you knap you gotta find this interesting!
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Here are a couple pic. Also everyone should understand this is only one firing and needs to be done many times to have solid data but what I am finding is very interesting if it repeats. Below are pictures of the pyrometer and what the fire pit looks like now.
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Sitting at 500 degrees photo of chart below
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This is about 24 hours at 500 since wood was added to the fire. This is crazy.
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Cool! I got to watch em. Hope you post pics and written info and not just vids tomorrow after the uncovering. I won't be back here til Sunday. Cool Stuff John, dpg
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Good stuff indeed. Thanks much for the information
;)
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Im truely without words as of 8:39pm it reads 501 degrees. I never would have guess this would happen!
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Ok I would be doubting this post based on my pit firing experence and wood firing. I am telling you guys this is real no kidding around on this test. I just went out to check and it is 503 the time here 9:39pm I am going to stay up as long as I can recording but this is unreal. Before I take the flakes out I will record fire size and depth of sand again. I think we need to have more info to reproduce this kind of high quality heat control.
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Forgot to add I did not beleive the pyrometer so I put my hand over the fire and it is hot.
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Forgot to add I did not beleive the pyrometer so I put my hand over the fire and it is hot.
Bust out the Hersheys bars, graham crackers, and marshmallows...it's s'mores time!
S'mores and burlington chert!
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10:30pm
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I have a surface temp reader and it sees 187. So I do believe that below the ash it could be 500 degrees.
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11:17 ...508 degrees
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I was just thinking that the fire you build over the pit is not for the purpose of heat treating the chert but rather a process that creates charcoal. It is this charcoal that fuels a long and even burn that lasts for hours and hours trapped between sand and insulating ash above. This ash blanket holds heat in and allows oxygen to enter slowly so it burns effeciently (because charcoal is more pure than wood) over a long period of time.
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513 degrees and it is 12:28
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Just wondering if anyone has ever done this on PA with a pyrometer.
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Well it is 1am I am going to bed and the pit is at 512 degrees. It blows my mind that this crude process can hold a material within 20 degrees for hours and hours...how smart they were.
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6 am see pic
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As soon as my phone gets a little charge I will make a video of the infrared meter going over the surface. It would be the only way I would believe this post.
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In trying to find answers I found this website http://flintknapper.com/Heat%20Treating.htm (http://flintknapper.com/Heat%20Treating.htm)
It says that it took three days for their pit to cool. So maybe this is not too far off base
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Well I shot a video but Derick wanted reading with photos so he could follow along.
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Simply amazing. Who would have thought the fire would last this long :o
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Here is the current temp
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Simply amazing. Who would have thought the fire would last this long :o
I wish I did then I would have gotten a little sleep lol.
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As you saw in the video the flakes are thin so there should be a good cook on this stone if I did not crack it during the ramp up.
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8:24 temp 528 surface temp 168. Looks like the surface temp drops as internal temp continue to go up. Maybe as the charcoal burns it create more insulation.
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Other stuff to think about. My pit was dug from the pit of many fires. This rim mound and wall are composed of crushed burnt clay earth ash and unburnt particle of charcoal. As the fire heated the wall and mound it burnt out any unburnt charcoal pieces and thus created dead air spaces. This may also contribute to the efficiency of this firing.
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I am doing this again sometime this summer for sure with a much larger pit and more stone it is more fun than loading a kiln.
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Wow. Like my wife would say, "It's Crazy Town in the pit". Don't think you'll be collecting your chert today either. Gotta go, thanks for the pics. dp
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Just a thought, but is the temp being held because of the temp of the rocks? Since they are so well insulated, maybe they are holding their heat really well. Can't wait to see how it has affected the rock.
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Just when you think you understand whats happening then this
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Time 11:06 temp 566
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thank you for putting videos together I'm looking forward to having the time to sit down and watch them
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11:30am 570
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Just when you think you understand whats happening then this
... :o ???
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Well check this out. For those who dont know about 6pm on wed the last of the wood was added to the fire.
1:40pm I am going to replace the battery and make sure it is reading correctly. Also I will test this with the oven and make sure it is giving correct reading. I will have to wait to tesr untill after the firing.
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When science meets primitive you realize that primative might be simple but it also does it's job :o. Can hardly wait to see the results.
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2:23pm and dropping now to 574.
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When science meets primitive you realize that primitive might be simple but it also does it's job :o. Can hardly wait to see the results.
I know how you feel but very concerned about the fast rate of climb in the beginning. Even if it is cracked we will learn a lot from this.
First the color will be interesting to see
Second the texture will still be able to be analyzed
Not to mention what we learned about how the fire functions by producing charcoal and ash this combined with the sand created a perfect atmosphere that brought the chert to our target temp of 600 or very near it.
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6:45 temp 577
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8:58 core temp 573 and surface temp is 140
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10:29 temp 565 and it look like it is falling
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How long since you added any fuel to the fire?
Has the fire burned out and if so, how long ago?
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Wednesday at around 6pm was the last time fuel was added to the fire. I believe that the coals were burning still when I went to bed on friday night. These numbers indicate the temp below 2"of sand therefore the temp above must be like between 800-600. This would suggest that the fire was continuing to burn. I am going out to check it now will post temp in a few minutes.
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To my disbelief but I do feel heat from the top. I told Josh Barnes last night that this post is making me look really bad because the data sounds unbelievable. I personnally dont know how this is even possible.
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I will redo this in the coming week (myth bust my on data) to see if it really can be repeated.
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Maybe I will order another pyrometer and run them at the same time. One can be places with the flint and the other at the surface just above the sand to help answer JWs question.
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Food for thought... If I did not have a pyrometer on the project then the following might have happened...I would have walked out and place my hand above the fire, having felt a surface temp of 140-120 decided that the flint must be cooler. With this thought yesterday I would have scooped away the ash to discover that the fire was still going and the sand still hot. I would have destroyed the delicate insulating barrier of the ash and cause the flint to prematurely cool. the chert may have been distroied. Perhaps falure by many who have tried this in the past may be linked to this "false" but logical conclusion.
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Many reading this post might say well I have built campfires and it doesn't burn past noon the next day (including me) or they might say I have burned large brush fires that only burn a day or so but my fire is designed very differently and entire structure of the pit would be different than those examples.
My modern kiln is constructed with a very light wt fire brick. This brick has many air pockets and is highly efficient. My fire in the backyard is a primitive rendition of the modern day kiln in its construction. Perhaps the ability of my design prevents rapid cooling and bakes/cooks the charcoal and allow a complete combustion of material in the fire place. We have all seen the charcoal that remains in the pit of the fire yes? Perhaps this is the fuel that is burning very Slowly and in an enviroment that is efficient in two ways. First it allows limit oxygen to reach the fuel second it retain to a high degree energy produced by the combustion to keep the fuel hot while the fire continues to burn lower and low toward the sand.
The ability of the fire to retain heat and thus continue to consume fuel must be aided by a highly efficient design.
So as I suggested in an earlier post the pit was constrcted on the site of an earlier pit. In fact I have been building fires on this spot for years in effect seasoning the material that will make up the floor and wall of the pit. The next couple of post will cover the initial composition and their transformative quality of this material as it is fired.
..I should have written all of this in an article and gotten paid for it lol.
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I will take this line of thinking one step further and suggest that fires in their homes would have used this technology to reduce the use of fuel. Here is a fire that will produce heat for days and is not smoky. I would use this in my hut or structure rather than a raging smoky fire. I wonder how warm a small structure could be kept using this kind of technology.
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Ok so here is how a house/hide sturcture could be kept warm and smoke free. Fire is created outside the tent and charcoal transfered to inside of the tent. Once the coals ignite the charcoal would burn with much less smoke than wood as ash formed over the charcoal a long slow burn would continue for days as my fire has if the structure of the pit was simular.
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It has been suggested that a common fire pit may have been how heat treating rock was discovered , I've seen brush piles burn under dirt for days when the brush had been dozed up and let set long enough for the wood to die off and dry out.
When I was young we would build a fire and let it burn down during the day and them dig a shallow pit beside the fire and pull the hot sand into the pit and cover with a thin layer of dry cooler sand and sleep on that spot on cold nights with just a light sleeping bag and stay warm all night even with a heavy frost on everything .
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Pictured below clay with small charcoal pieces and burnt clay without charcoal. The first picture has the samples oriented in a manor that reflects there location in the pit This was what the pit was constructed and shaped with. The other sample show the material transformed into a light wt and fluffy material with a high insulative quality.
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In the third picture one can see pieces of charcoal in the sample. I pulled one piece to the right side and middle of photo.
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Is anyone finding this post interesting? I think it is mind blowing data. I cant wait to do it again!
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8:52 temp 518 so now we are dropping and at a nice rate. By tonight we should be looking at some cooked flint.
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I uncover heat treated chert 48 hours after the last fuel (charcoal) has been added to the fire. Don't know the temps then - it will still be pretty warm but won't burn the hands. Rick B
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9:55am temp 509 so it appears that we are dropping 5 degrees per hour for now.
@ Rick B did you dig a pit? If so it would be interesting to know if it was located in the same spot as a previous campfire or better yet pit because that would cause the particles to be mixed.
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Is anyone finding this post interesting? I think it is mind blowing data. I cant wait to do it again!
I have been checking in. This is good information. I have some chert that I found the other day I think. I will use this to do some baking of rock myself ;)
Thanks for posting this.
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@T.H. Your very welcome just remember to dig a pit build a fire and once it is out mix all of the loose dirt with the charcoal to made a new pit from. I believe this is why it has cooked the way it did.
The time is 1:06 temp 480 degrees about 7 degree drop per hour. That is a very slow downward ramp.
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Hopefully we'll be able to see some of the finished product tomorrow night or so! This has answered a lot of questions I had about heat treating with fire, but I think it might have created more new questions than it answered. I didn't make it home this weekend, but when I do, I will dig me a fire pit and have a few fires to try to recreate this experiment. I might even splurge on a pyrometer! Shhh! Don't tell my wife. Josh
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In case you guys forgot this chert broken or not will be his as soon as our paths cross. I through a couple in for me but he gets all of those you saw in the video. So Josh it's up to you to pull this post up and give use your thoughts on quality good or bad.
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82 dollars just search k2 pyrometer.
I will do this again next week it is a very simple process and looks fool proof to me. I will re measure the sand depth so all of you will have a starting point for a 600 degree fire. Just remember the fire may climb toward the end.
Josh if you do this will you please keep notes so we can compare?
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I have not read anywhere a description that defines the qualities of the pit built the way I did so unless someone has a name for the "pit preparation" I would like to call it a" JW Pit" because he is the funnest guy I know and you never know what he will say next. This was the funnest firing I have ever done and I never new for sure what was going to happen next!
So defined ...A JW Pit is a pit constructed in such a way as to have the remains of material from soil that consist of but not limited to, clay, small rock, sand, and charcoal, from previous fires mixed together. This material makes up the walls of the pit and as the firing burns out the charcoal it leaves ash. The remaining material and air pockets then becomes an important element in retaining heat during the firing and cooling.
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John, I've tried digging a pit before but have had problems with moisture seeping up through the ground. We've had 18 straight days with rain here in Columbia SC so the only way I could do it outside now would be in my washtub. Here's a link to your thread from last year when I commented on what I use to heat treat - see the photos. Rick B
http://www.primitivearcher.com/smf/index.php/topic,33532.msg442786.html#msg442786
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John, I've tried digging a pit before but have had problems with moisture seeping up through the ground. We've had 18 straight days with rain here in Columbia SC so the only way I could do it outside now would be in my washtub. Here's a link to your thread from last year when I commented on what I use to heat treat - see the photos. Rick B
http://www.primitivearcher.com/smf/index.php/topic,33532.msg442786.html#msg442786
Good info on that thread! Where does the time go lol. I gathered that sand and sifted it as you said and parked in the garage until I started this post wow. Too mant projects too little time. Again thanks for the help.
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8:23 temp 321
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5:91 am 182 degrees. I am going to let it cool before I pull it out.
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Interesting thing to think about is the dropping rate of the fire which is about 15-20 degrees per hour. This is equal to a packed kiln if not better.
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Can hardly wait to see your findings. :)
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I am headed home right now to check it
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Curious to see how it turns out for you. I heat all of my rock in a pit under a fire. took a little trial and error to figure it out but I never went to the effort that you have with the meter and such. mine has always been pretty straight forward. bury 2-4 inches in dry sand depending on type of rock I'm heating, start a slow fire and build it to have good even coverage. I keep burning about 6-8 hours (depending on type of rock, some take longer and hotter than others). Then I let it go out and go to bed. The next morning there are still red coals under the ash and I let them completely burn out which is usually by noon the day after initial firing. once the embers are out, I scrape off the ash layer, but not the sand. by evening I can take the rock out and it's fully cooked and glassy. I have made the mistake before of letting it cook too long or too hot and ended up with broken or really weak rock. Your method is a bit different so I'm curious if there is much difference in the end result. I have liked the open fire as well b\c I can multi task and fire some pottery while I am at it. been really wanting to cook rock here lately, but summer in FL..... Rains every day! good luck! I read through but I think I overlooked the type of rock you are cooking. I probably read it and forgot already..lol so what flavor are you cookin?
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Ok the pit was at 130 and I could not wait so here is the group photo of the rocks from the pit. Not one crack all were great and intacked! The follow in goup of pictures will be details of the rocks and a little knapping and some pictures of the recovery
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First color change photos.
These two spalls were from the same larger rock. The whiter one is cooked
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You can compare color change in these two pictures.
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These two picture are also before and after giving a pick shade to the stone
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These to flakes represent how the white chert changes when fired. The firing makes the stone loose the blue grey on left and turn pure white on right.
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Cool photo my wife took! She took all of the photos because she is amazing!
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Photo of heat treated white and how some of it has a light pick shade.
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Seems to flake well on this sneek peek with the pressure flaker.
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This flake was tested for edge to edge flaking
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I really wanted at this point to make a point but knew many were waiting for the pictures and the end of the story.
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Now boring pictures of me uncovering flakes. There were 3 inches of ash sitting on top of the sand.
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I discoverd complete burn of charcoal in the center but just on the edge it did not and that kind confirms for me the reason for the long burn.
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Pictures of the stone being removed and a very happy knapper.
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I really enjoyed sharing my first pit firing with all of you here on-line but it is very important to recognize those who contributed to the success of this project
. I am not the smart guy here on PA what I have learned about how to do this came from the help of the following
John Whittaker's book on knapping
JW ..he is a real smart guy and funny
Josh Barnes
Scott stanberry
Tower
Jackcrafty
Mullet
Rick B
Jcinpc
Cowbow
And all that gave input on this post.
Thanks guys you made this week a lot of fun!
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Hey Rick B thanks for your input on this project. I am the kinda guy that wants to know the why in why does it work so the data just answers the hundreds of question that pop in my head. But the next time I will approach it like you and just do it because it works that way lol. The stone is Burlington.
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Forgot this picture
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Man....that stuff looks nice! I believe the thanks goes the other way though John. Not just because I'm gonna get some new material to work, but because of your detailed data posting throughout the process. I now have an idea of where to start on treating some of the tough stone I have laying around. Thank you very much! Josh
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Great post! I'm a believer in pit cooking. I loved cooking rocks Abo style. Living in town has busted me down to 2 turkey roasters. Well done Sir.
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Great post.
Thanks much for the information posted. This will be used by me ;)
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Good post, John. Just got a chance to read the whole thing. Well done!
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Awesome thread! 8)
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Thanks guys for the comments! I am going to make a couple points and on this thread so stay tuned for an update in the near future.
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Followed the progress all the way through. Gooood stuff! How about adding a couple pics of the finished products. Thanks.
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My dial-up went out on Saturday morning. >:( Got to my high speed spot and got to read thru 4 pages! Good stuff John. I'll try me a JW pit next time I cook some stone. Can't wait to see the next firings results too. dp
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I think I sometimes think too much but if you know me then you know it's what I enjoy doing.
So here goes the thinking...an old knapper returns to his heat treating pit where he has set up camp for the next few days to heat treat chert. He has fond memories of his grandfather letting him start the fire as his father arranges bifaces by size that will be going into the fire. His brother older in years continues knocking out bifaces that will be included in the firing this time. It is mid summer on a hill top and the grass has not browned yet due to the drier days of summer.
His day dream is interupted as his sons are returning to camp with the last of the sand and wood that will be used for their fire this time and for the first time he will be passing on his knowledge to others that will join in on this opportunity. He runs the event now after his father pasted during the winter.
The week has been filled with heavy lifting but made easier because the camp is located close to a quarry of fine chert located in the valley. With all of the materials assembled he prepares the pit that is raised from deposits of sand and flakes of chert and charcoal from generations of knappers.
My point is that the mound of sand and ash would amount to a pit that would be above grade and constucted partly from sand. This sandy ground would drain quickly and dry fast.
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I wrote the story below because Rick B got me to think about how my pit is going to fill with water when it rains. Hmmmm I need to do more firings. Deep pits below grade and repeated use do not make sense together.
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Well John I really enjoyed going through this one! I always intended to do a story on cooking rock in the ground just never got one of those round tuits :). Been a long while since I've done that. You've got me wanting to get home and fire it up. The temps are very interesting.
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Yes please do it again and come back to this post and list the data. My temps were hard to believe but I am going to do it again and see if it is repeatable.
If any one else want to record data on this post please do so because the search tool on the is site is not good. It will create a bank of knowledge for others wanting to try this.
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I managed to swing by John's place today for a short visit. He hooked me up with some spalls from this batch. I couldn't resist trying it out. Man! Is this nice stone! I'm lovin this stuff! Thanks John! Josh
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Nice work Josh! Looks like he got the right cook on it for sure.
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Great job! Thanks! Now the next time, put in a cut up hog, wrapped in foil, with onions, and garlic, and carrots, and some mojo sauce. Mmmmmmm, rockin hog!
Wayne
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Very good article, lots of pics and good explanations. I live in Alabama, like Twisted Limbs, I have problems firing due to moisture in the ground. What I do is dig a shallow pit, mound the sandy dirt around the side and build a green wood bonfire. I let it burn down to coals, then push my mounded sides over the coals to dry out. That usually takes a day and a night. I uncover it the next day and let the coals burn out, that afternoon, I bury my preforms or mostly just rocks, then build up a dry wood bonfire. I let it burn down and go off and leave it for the next couple or three days. I put a piece of tin over it to protect it from the rain, but if it rains, you can expect to loose a lot.