In flint knapping, why do you have to fire the flint?

Question

In flint knapping, why do you have to fire the flint?

Answer 1

Because it would make sense...  

Answer 2

Heating or firing flint nodules helps to re-align the crystalline structure and permits finer knapping.

Interesting question.

Answer 3

Firing or heating the flint makes it harder.  Hardening serves two purposes. Of course the obvious is to make it harder.  But once it is hardened, the knapper can then make more concentrated chips for the final form.  Prior to hardening, larger chunks would be knapped away making it difficult to chip out a more streamlined or straight edge.

My grandfather would also dig another hole in the ground and bake his finished points again.