A window constructed using the dalle de verre (glass slab) technique has large, thick chunks of glass set into concrete or (more commonly today) an epoxy resin.
The slabs are shaped by chipping away with a hammer. This not only yields the traditional "rough" shape to the glass, it usually leaves the edges with attractive facets. In fact, dalle de verre is sometimes referred to as "faceted glass".
Modern development of this technique is credited to Auguste Labouret and Pierre Chaudiere who worked together in France during the 1930s.