The mural spaces available for fresco decoration having been gradually suppressed, and decorative painting limited to the illumination of certain subordinate members of the structure, the mediæval artists began to apply themselves to the decoration of the great screens of glass which, with their sculptured framework of stone, now filled the entire spaces between the piers. In this new art, or rather this incarnation of the spirit of decoration under a new form, we find a fresh illustration of that supple assimilative genius which already distinguished the French artist. [Illustration: 119, 120. PAINTED WINDOWS OF THE EARLY TWELFTH CENTURY. FROM ST. RÉMI AT RHEIMS[41]] [41] Drawings lent by M. Ed. Didron, painter upon glass. "It is in the nature of the material used, that painted windows should greatly affect the character of the building they decorate. If their treatment is injudicious, the intended architectural effect may be greatly modified; if, on the other hand, they are intelligently applied, they tend to bring out the beauty of structural surroundings.... As is the case with all architectonic painting, stained glass demands simplicity in composition, sobriety in execution, and an avoidance of naturalistic imitation. It should aim neither at illusion nor perspective. Its scheme of colour should be frank, energetic, comprising few tints, yet producing a harmony at once sumptuous and soothing, which should compel attention, but seeks not to engross it to the detriment of the setting. Like a mural mosaic, an Eastern carpet, or the enamelled goldsmith's work of the twelfth and thirteenth centuries, a truly decorative window has no affinities with a picture, a scene or landscape gazed at from an open window, where the interest concentrates itself upon a particular point, and where the illumination is not equally diffused throughout. The fundamental law of decorative painting rests on a convention the aim of which is the satisfaction of the eye, which finds its pleasure to a far greater degree in the logical decoration of some structural or useful object than in its realisation of natural phenomena. Between painted windows and pictures a great gulf is fixed; and the modern school, the heir of the Italian Renascence, seeking to bridge it over, has seduced decorative art from the safe paths of sound judgment."[42] [42] _Le Vitrail à l'Exposition de 1889_, by Ed. Didron; Paris, 1890. [Illustration: 121. PAINTED WINDOW OF THE TWELFTH CENTURY. CHURCH OF BONLIEU (CREUSE)] [Illustration: 122. PAINTED WINDOW OF THE THIRTEENTH CENTURY. CHARTRES CATHEDRAL]