Anyone who has seen a Jan van Eyck painting up close will be in no doubt of his brilliance at depicting every inch of detail in luminous oils. He perfected the medium. But few people would have had the opportunity to see van Eyck’s draftsmanship in person. Only one van Eyck drawing survives: “Portrait of an Older Man,” in the Kupferstich-Kabinett in Dresden, Germany. Over 580 years old, the drawing in goldpoint and silverpoint, is the earliest study attributed to a Northern European artist. Van Eyck autographed the work, making it the only drawing universally accepted as signed by the artist. Due to the drawing’s fragility, it’s rarely displayed. Remarkably, this exceptional drawing is now on U.S. soil and is on display at The Morgan Library & Museum through mid-January, as part of a special exhibition.  “Van Eyck to Mondrian: 300 Years of Collecting in Dresden” celebrates the 300th anniversary …