Pomona looked at the picture frame in the Clock Tower storeroom. It was completely empty, with neither landscape nor portrait inside.
Yet it had once been the "cage" that held Phoebe in the Portrait Curse. Bill had even thought it had been cast with an advanced Extension Charm.
It was hardly strange that he had come to that mistaken conclusion. Many of the oil paintings on Hogwarts' Grand Staircase dated from the Renaissance or the late Middle Ages. By then, perspective and three-dimensionality had emerged, making them vastly different from the flat paintings of the early Middle Ages.
Religious paintings used gold extensively, not only for saints or the halos above holy figures' heads, but also as backgrounds, symbolizing eternal happiness. For instance, in that Florentine painting of Jesus crucified upon the Tree of Life, the upper portion representing Heaven was gold, while the lower portion was black.
God-centered art hoped viewers would see beyond material things to their spiritual meaning—the reality Plato spoke of. Artificial perspective, meanwhile, signified the secularization of the visible world. The center of a painting was no longer God and the transcendence He represented. The frame became like a transparent window through which one could see what the artist wished to depict, largely from a human perspective.
Take Andre Pozzo, the Baroque master of illusion. When one stood directly beneath the dome he painted and looked up, one would discover how impoverished human language was. This illusion differed from the weather magic on Hogwarts' Great Hall ceiling, which matched the weather outside. Those ingenious visual deceptions made viewers forget that they were merely man-made objects, forget the artwork's existence as an object in the world.
To make an image feel real, painters used black for shadows—something that had not been permitted in paintings of the