Another great bread by Peter Reinhart, The Bread Baker's Apprentice. This is his "window pane" tip for testing if the dough is ready: Pinch off about two tablespoons of dough and try to stretch it into a thin membrane (windowpane). If you can do so without tearing, but the membrane is mostly opaque, you have barely developed gluten. If you can stretch a paper-thin, very translucent windowpane, the gluten is fully developed. A medium level is in between these two extremes: the windowpane is translucent with some opaque areas.