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How to Thermal-Treat Stones

Many colored gem stones -- for example blue diamonds -- are heated to enhance their color. Bluestone pavers are often heat treated to make their surfaces smoother. But throughout human history, the stones that were most often thermal-treated were stones like flint, quartz and chert that were knapped or chipped to make stone tools. Heating these hard stones alters their crystalline structure making them denser, easier to fracture and easier to work. Experimental archaeologists often borrow from the experience of gemologists when trying to reproduce ancient artifacts and their experiments show that these stones should be heated and cooled very slowly.

Things You'll Need

1/4 inch thick flint, quartz or chert flakes
Dutch oven
Digital oven thermometer

Instructions

- 1
  Arrange 1/4 inch thick flint, quartz or chert flakes into a single, tightly fitting layer of stones on the bottom of a Dutch oven. Put the lid on. These stones sometimes explode when heated and the Dutch oven will contain the explosion.
- 2
  Put the probe of a digital oven thermometer in the oven and close the oven door. Put the oven on the lowest possible setting and wait one hour.
- 3
  Increase the oven temperature by 25 degrees Fahrenheit every hour, until the temperature reaches 275 degrees. The maximum temperature to which any of these stones can be heated varies greatly, not only by stone, but by the location at which the stones were mined. Some stones can be heated to over 500 degrees. The only way to determine the optimum temperature for thermal treating your stones is by experimentation.
- 4
  Bake the stones in the Dutch oven at 275 degrees for at least four hours, then turn off the stove and let the stones cool inside the Dutch oven.
- 5
  Remove the stones when the digital thermometer indicates that the oven has cooled to less than 130 degrees.

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