Heat Treat Your Stones

Heat treating the stones you are going to use for making a primitive knife or other stone tool so that the process is easier.

Heat treating weapons goes back a long way in time. However, did you ever imagine that it went back all the way to the Stone Age? I didn't think so either, but apparently ancient humans used heat treatment of their rock to improve the rock's quality.

Heating rock drives off electrons or something which somehow does something to the stone blah blah blah. I don't understand it, but apparently heat treating stone makes the rock somehow harder, stiffer and easier to flake. Flake means to chip off pieces of a stone to shape the stone into a tool, a knife blade for example.

To improve your rock for flint knapping, place your stones (hehe) in a fire for a long time. Eight hours seems about right. You want the fire to heat the blade to about 450 degrees F or higher depending on the type of rock. Experiment! So don't go crazy with the fire and drive the heat way up.

This heat treatment makes the stone harder, stiffer and more importantly it makes the stone more brittle. This brittle characteristic is important for people in much of the world that don't have access to the best rocks for chipping. With this technique you can take stone that is otherwise very difficult to chip and render it more brittle and this makes flint knapping of that stone much more likely to end with success instead of failure.

The heat treating of the stone may also improve the aesthetics of the stone.
Not all stone can be heat treated successfully.
Stone should not be thicker than a couple of inches.
Drying the rocks before treating them is important.
Dry the rocks not with a cloth, but instead by applying low heat for many hours to drive moisture out of the rock.
To dry heat to above boiling point of water and allow to cool. Repeat 4 times.
Ideally you want to heat the rock over many hours bringing up the temperature to approximately 450 degrees. Rapid temperature changes are not good.

When heating a rock to improve its properties (450ish degrees) you want the entire rock to heat and cool evenly. Packing it with sand or lots of other rocks will help maintain even heating and cooling. If this is not achieved there is the very real possibility that your rock will crack or break.

If you treated rocks keep cracking when knapping then it is possible you have too much moisture in the rock, it was overheated, or it is made of different materials that behave differently when fired.