What do you think of when you try to conceptualize nothingness? Is it the black depth of deep space? Or the emptiness of a white piece of paper?
For Escher, nothingness was gray. Escher said that gray is nothing and once gray either lightens to white or darkens to black then there is something. We can see everything in black and white. To Escher, and to a graphic artist, white was just important as black - the entire woodblock image is created by the positioning of white shapes next to black shapes. Escher illustrated this belief repeatedly throughout his career. He demonstrated this concept by printing the black and white prints in Regular Division of the Plane with gray borders around the image; the idea that white is just a background is erased. Nothing is gray.
The center of Verbum, the edges of Development and Encounter, the bottom of Liberation, the left and right margins of Metamorphosis II and III are all gray. The gray in the center of Verbum is so fuzzy that people often think there is something on the glass of the frame. I think Escher smiled every time someone paused to look closer at his creations.
The gray border forces the viewer to see that white has equal value as black in this symmetry work. Some of the Regular Division of the Plane works are available for purchase HERE.