On a frosty night last december, the couture salon at the Chanel headquarters on rue Cambon in Paris was transformed into a Byzantine mini-palace with gleaming gold and silver mosaic carpets, gold sequined walls, stained-glass tables, Ottoman chandeliers, glass candelabras, and couches covered in metallic silk fabrics. At Chanel, staging provides an essential environment to showcase a new collection. The décor each season compliments the mood of the clothes.     During a recent visit inside the Basilica di San Vitale in Ravenna, Mr. Karl Lagerfeld photographed the delicate mosaics on the walls and floors. (These pictures became a monograph on parchment recently published by Steidl called Byzantine Fragments.) Among the colorful mosaics on the...