Post by RickB on Oct 4, 2019 15:55:43 GMT -5
Here's my formula for heating rock to make arrowheads/blades. I may have posted some of this
back in 2010/11. There are formulas on the internet for cooking rock for flint knapping. The temps
and holding times will vary for each type of rock. Some rock changes color, others don't. This info
should work for heat treating rock for tumbling.
Here's a photo of my outdoor setup - it's a washtub and I call it my redneck grill, and you can see why from the first photo. I heat Savannah River Chert 3 to 4 inches down in the sand (each inch deeper equates to appx. 100 degrees cooler). Note: It is better to use clean sand and not dirt as you will get better heat conduction. 16lb bag of charcoal in the morning followed by another bag in the afternoon. Rock is finally cool enough to handle and comes out late afternoon of the third day. I use a piece of roofing tin to protect from wind and rain. Second photo is some chert and debitage along the front side of my shed. I'm currently using a turkey roaster, liner out, with clean sand (filled to the top). I put it on 250 degrees for a couple hours then slowly ramp it up to 450 - at 250, I've had steam condensing under the lid and sizzle when it falls back onto the hot sand. I now crack the lid a little to let it out when at 250. I drill two small holes in the lid of the roaster, one in a corner and one in the center. I place high-temperature grill thermometers in the holes during The entire process. Temperatures are higher in the corners, cooler in the center. I put thicker and rougher pieces in the corners, thinner pieces everywhere else. I let it go for about 48 hours before I turn the heat off. Let it cool to touch before you take the rock out. Have had good results this way. Last photo is a raw, unheated spall. Rick B
back in 2010/11. There are formulas on the internet for cooking rock for flint knapping. The temps
and holding times will vary for each type of rock. Some rock changes color, others don't. This info
should work for heat treating rock for tumbling.
Here's a photo of my outdoor setup - it's a washtub and I call it my redneck grill, and you can see why from the first photo. I heat Savannah River Chert 3 to 4 inches down in the sand (each inch deeper equates to appx. 100 degrees cooler). Note: It is better to use clean sand and not dirt as you will get better heat conduction. 16lb bag of charcoal in the morning followed by another bag in the afternoon. Rock is finally cool enough to handle and comes out late afternoon of the third day. I use a piece of roofing tin to protect from wind and rain. Second photo is some chert and debitage along the front side of my shed. I'm currently using a turkey roaster, liner out, with clean sand (filled to the top). I put it on 250 degrees for a couple hours then slowly ramp it up to 450 - at 250, I've had steam condensing under the lid and sizzle when it falls back onto the hot sand. I now crack the lid a little to let it out when at 250. I drill two small holes in the lid of the roaster, one in a corner and one in the center. I place high-temperature grill thermometers in the holes during The entire process. Temperatures are higher in the corners, cooler in the center. I put thicker and rougher pieces in the corners, thinner pieces everywhere else. I let it go for about 48 hours before I turn the heat off. Let it cool to touch before you take the rock out. Have had good results this way. Last photo is a raw, unheated spall. Rick B
... to the New Guys from The ChatBox V.2 Crew