While the metal is hot, securely hold the glass on a flat surface or hang it on the window attaching clip as shown here. Gently tap the frame using a small block of wood and a hammer to push the metal frame away from the glass edge. A 2x4-inch piece of wood about four or five inches long will work well. Work your way from one edge to the other, and be careful not to hit the glass with the hammer. It's OK if the wood touches the glass while the frame is being tapped out.