Seeing Is Believing

That convex mirror in the Arnolfini Portrait does more than decorate the wall. It curves the whole room into a single reflection, including figures the viewer cannot otherwise see — a trick of optics that fascinated later painters and, eventually, photographers.

This is the heart of the Northern method: prove a spiritual truth by getting the physical world exactly right. Detailed observation became its own form of devotion, and that habit of looking hard leads straight to Dutch Golden Age painting centuries later.