As the host opens the door, guests in jeans enter, slap palms with the host, call out “Hey!” and find a place to sit, or maybe head to the backyard grill. Social gatherings are casual affairs today. Most people don’t attend formal functions often, much less with “important people.” To be invited to an event…

Though created nearly six centuries ago, the justly famed double portrait by the Flemish master Jan van Eyck in the National Gallery, London, still holds viewers in thrall. Yet art historians have been unable to determine with certainty who is depicted or what the circumstances and intent of its creation were. The first in-depth analysis…