The first truly great masterpiece to demonstrate the possibilities available when working with oil paint, so they say, was the van Eyck brothers’ Altarpiece of Ghent. (The elder brother, Hubert, apparently did the general design, and his brother Jan painted it after the brother’s death.) I ran across a reference during my studies of the history of Belgium, and found it interesting, though it is (at present) very unlikely to turn up in my novel. A little research turned up a few worthwhile links, though: Here’s an NPR piece on it (supposedly) being the most stolen artwork in history, and …