Author Topic: Heat treating chert with fire, (another thought)  (Read 25706 times)

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Offline iowabow

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Heat treating chert with fire, (another thought)
« on: July 11, 2013, 11:07:06 am »
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)
« Last Edit: July 15, 2013, 09:25:05 pm by iowabow »
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Offline iowabow

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Re: Heat treating chert with fire, update
« Reply #1 on: July 11, 2013, 11:09:56 am »
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.
« Last Edit: July 11, 2013, 11:15:31 am by iowabow »
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Offline Dalton Knapper

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Re: Heat treating chert with fire, update
« Reply #2 on: July 11, 2013, 12:08:53 pm »
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?

Offline iowabow

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Re: Heat treating chert with fire, update
« Reply #3 on: July 11, 2013, 12:29:05 pm »
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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Offline iowabow

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Re: Heat treating chert with fire, update
« Reply #4 on: July 11, 2013, 12:32:26 pm »
The fire continued for hours inside
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Offline iowabow

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Re: Heat treating chert with fire, update
« Reply #5 on: July 11, 2013, 12:37:34 pm »
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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Offline iowabow

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Re: Heat treating chert with fire, update
« Reply #6 on: July 11, 2013, 12:40:06 pm »
This was a picture of that storm.
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Offline iowabow

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Re: Heat treating chert with fire, update
« Reply #7 on: July 11, 2013, 12:55:37 pm »
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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Offline bowtarist

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Re: Heat treating chert with fire, update
« Reply #8 on: July 11, 2013, 01:13:29 pm »
Good Stuff John! I'll have to find a high-speed connection soon to watch all these vids.  ;) dpg
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Offline Josh B

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Re: Heat treating chert with fire, update
« Reply #9 on: July 11, 2013, 01:48:38 pm »
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

Offline iowabow

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Re: Heat treating chert with fire, update
« Reply #10 on: July 11, 2013, 01:52:49 pm »
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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Offline iowabow

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Re: Heat treating chert with fire, update
« Reply #11 on: July 11, 2013, 04:22:12 pm »
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
Video #2 http://youtu.be/niwvZh19Y7Y
video #3 http://youtu.be/JcVO_hvsERs
video #4 http://youtu.be/R8kboAVe6Jg

« Last Edit: July 11, 2013, 04:55:39 pm by iowabow »
(:::.) The ABO path is a new frontier to the past!

Offline Outbackbob48

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Re: Heat treating chert with fire, update
« Reply #12 on: July 11, 2013, 04:23:14 pm »
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

Offline iowabow

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Re: Heat treating chert with fire, (videos added)
« Reply #13 on: July 11, 2013, 04:45:48 pm »
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.
« Last Edit: July 11, 2013, 04:51:43 pm by iowabow »
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Offline twisted hickory

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Re: Heat treating chert with fire, update
« Reply #14 on: July 11, 2013, 05:16:03 pm »
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
Video #2 http://youtu.be/niwvZh19Y7Y
video #3 http://youtu.be/JcVO_hvsERs
video #4 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