Select potatoes of equal size, so that they will all bake in the same
length of time; wash them and bake them in an insulated oven with the
stones heated till the paper is a golden brown as explained in the test
on page 225. Good-sized potatoes (eight ounces) should bake about
forty-five minutes. Lay them on a rack to prevent them from touching the
hot stone. They will bake better than in an ordinary oven.