Using a backing hammer, begin at the side farthest from you and slowly, applying pressure, roll the hammer from the center of the spine to the edge. You want the hammer's edge to line up with the edge of the spine on each stroke.
(roll from center to edge, lining up hammer/spine edges.) |
Turn and do the same thing in the other direction, rounding the spine from the center to the edge until both sides have been evenly rounded. Then using a gentle tapping motion even out the lines created by doing this. You should end up with a spine rounded over the sides to form a dome almost like a mushroom.