colibri
off to a rocking start
Member since July 2018
Posts: 8
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Post by colibri on Aug 3, 2018 20:55:52 GMT -5
i recently bought an old electric roaster oven off of craigslist to experiment with heat treating some flint ridge material i recently harvested. I want to know if it will bring out more color in these tumbled and polished pieces. these are all “before” pics. i also want to see the color change in these larger raw chunks AND I’m hoping these knapping pieces will flake more easily and maybe have more color as well. here’s my recipe: i first alternated layers of rock with sand into the roaster. then . . . 250* for 6 hrs. then gradually raising temp 25*/hr til you get to 500* then leaving it there for +/-14 hrs. then easing the temp slowly back down and letting it completely cool before handling. I’ve been having some trouble getting the old roaster oven to stay at temp. maybe something wrong with the thermostat. It’s an older model but I bought it because it goes up to 500 degrees. all the newer models cap out at 450 degrees. Anyway, stay tuned to see how it turns out. should have results up in a day or two.
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colibri
off to a rocking start
Member since July 2018
Posts: 8
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Post by colibri on Aug 4, 2018 14:40:48 GMT -5
here are the current results of the heat treating experiment with flint ridge flint. before heating: after heating: these tumbled and polished flints got significantly redder. but i noticed that the yellows almost disappeared and the semi-translucent chalcedony became much more solid white and opaque. overall this makes for less interesting color dynamics and less depth within the pieces. i don’t think i’ll do that again. before heating: after heating: these are some of the chunks i harvested at the Nethers farm. again, they got redder but the yellows are lost as well as some of the purples in the pieces on top. just generally less dynamic. also, these cooked pieces are likely much more brittle which could make them harder to tumble or cab. probably wouldn’t do this again. before heating: after heating: these chunks and flakes i harvested for flint knapping. you can see the pinks and reds popping on what had largely been grey and drab material. i haven’t had a chance to test and see if the flakes are easier to knock off yet but I do think the color is quite an improvement over the solid light and dark grey. with increased color as well as (assumed) improved knapability, i would definitely do this again. thanks for checking this out. any comments, questions or suggestions are welcome!
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mjflinty
spending too much on rocks
Member since September 2011
Posts: 358
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Post by mjflinty on Aug 4, 2018 16:40:20 GMT -5
For flintknapping, the average temps to heat treat Ohio Flint Ridge Flint range between 600 and 675 degrees. Most turkey roasters don't get that hot so a pottery kiln is used. I'm sure you'll find the pieces in the corners of the roaster will redden some but, that will only be a few millimeters deep. Cool experiment nonetheless.
All the best, Michael
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Post by orrum on Aug 4, 2018 17:01:14 GMT -5
X2 Michael. Take the pan out of the roaster. Put the flint right on the metal bottom and stack it full with no sand. Put larger pieces in votners, they get hotter. After putting your flint into the roaster poor it full of clay base kitty litter. Put fiberglass insulation on top of kitty litter to fill up roaster and the lid. Use big scrap rocks to weight down lid. You should get above 500 this way. You can treat twice or even three times and improve knappability. 650 is better but we do as we can. Try after it cools soaking in wster for a week and then take it out and let it dry. This sometimes helps knapping. Warning Will Rogers warning!!! Flint ridge lays in layers. You either have to saw the layers apart or knapp into layers. When digging you can often chisel it up in layers. Warning, it will rope a copper bopper up cause you have to swing for the fence!!! You need speed and weight into your swing!
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Post by RickB on Aug 5, 2018 15:07:34 GMT -5
Nice formula Orrum. To get an accurate read on the temperature, I drill a small hole in the center of the lid and one of the corners and place a high temperature thermometer in each hole. I use playground sand and no insulation. Have gotten temps over 600. Rick B
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