I did, once, consider knapping my own but did not carry on with it. While I was looking into it I found this snippet that might be useful for anyone who does want to give it a go.
Flint - Brought slowly to a temperature of 150 deg. C to 260 deg. C, (300 deg F to 500 deg. F), for 24 hours, then slowly cooled to room temperature.
This make the material more homogenous and thus more "knappable" and produces tools with a cleaner, sharper cutting edge.