July, 1980 This was one of our very first attempts at heat treating in a pit. Most of the material is Regular Crescent Quarry Burlington. This is how the flint was arranged in the pit, with larger blanks toward the center and smaller toward the outside. After this photo, the blanks were covered with 2 inches of dry sand and the fire was started. Firewood was added slowly and kept burning for about 6 hours.
The pit before the second 2 inch layer of sand. November, 1982
The fire with beer cans in place.
Covering the fire with corrugated tin. Notice the size of the firewood being used. The firewood was built up, for the final time, the next morning. Then, the fire was covered until it burned itself out. That usually took about 12 hours.
No date, probably 1982 or 83. Note the pile of sheet metal in the background. It is imperative that no rain hits the flint while it is being heated or cooling down (3 days usually) so the sheet metal is thrown over the fire pit. This not only protects the flint from rain but also helps to drive the heat downward near the end of the heating period.
May, 1983. Notice how the ash has accumulated. This ash will be much thicker if softwoods are used and the flint will be somewhat insulated. Hardwoods are preferred. As you can see, the clay around the pit gets fired to a very red-orange color. If we find heat-treating pits archaeologically, they should be heavily burned around the perimeter.
Heating in a bathtub. The bathtub allows the fire to be built surrounding the rock. You need to be careful to control the amount of firewood as it's very easy to over-heat with this method. Note how the cast iron pipes, used to suspend the bathtub, are bent from the heat. In the background, is the firewood pile. Larry uses about that much firewood for each treating.
November, 1989. About a 5 to 20 percent breakage rate is common in heat-treating but, as time goes on and experience takes hold, breakage can be controlled to 1 to 5 percent. Make sure the rock has dried for at least a week to remove internal water which will turn to steam, when heated. Be patient and observe which rock takes more heat and which take less. In other words, experiment.
You will quickly find that some cherts take more heat than others. For instance, Burlington usually needs to be heated to over 550 degrees for best results while Kaolin can't take more than about 350 or 400 degrees.
Larry has an old pottery kiln now and is able to control the heat much better than he used to. He sure misses those old heat-treating parties, though. Back in the good ole days we heated flint, fired pottery, drank beer, ate hot dogs and chili, and socialized around that old fire. Larry made many life-long friends while sitting around those heat-treating fires.