Get a metal pot with a lid, put some dry sand in it and bury a small chunk of rock in the sand. Put it on 200 for a couple of hours after supper and before you go to bed, crank it up to 450-500. When you get up in the morning, turn the stove off. Your rock will be cool enough to check and to try to knapp that afternoon. See if it improves the rock, if it does, buy a toaster oven for the garage or shop and start cooking.