Theophilus explains the long process involved in the creation of stained glass. The vibrant colors were generated by way of both chemistry and alchemy. Patterns were often used, upon which sheets of colored glass were cut by a process of controlled breakage. When all the pieces were assembled, they were soldered together in lead cames. Then the glass figures were painted in two stages, fired, and weatherproofed. Finally the images were fitted into panels and then into the architecture supporting the glass. As architecture evolved, so did stained glass. In the twelfth century, stained glass was fitted into relatively small lancet windows, and stylistically often had borders around the glass which emphasizing the distinction between the windows and the architecture. Within a hundred years, however, architectural technology allowed stained glass to comprise nearly all the wall surface of buildings. At this point, stained glass became more narrative in composition, often using artistic conventions from other media to lead the viewer's eye across numerous lancets. In the later Middle Ages, grisaille glass, white glass painted in shades of monochromatic gray and less figure-oriented, was popular.