There are two main methods of doing plique a jour. The easiest and the one most usually found in books is to place the pierced metal on a sheet of mica or platinum foil and fill the holes to the top with enamel. As the enamel shrinks a bit when fired, the holes are topped up and refired until the holes are closed up. Then the mica is removed, the metal cleaned and the piece refired without any backing. This works, but the enamel will be the same thickness all across the hole and cannot let as much light through as method 2.