How can a flat printing stone hold ink in some places but repel it in others?

A printing stone can carry a detailed image while remaining essentially flat. This seems surprising if printing is imagined as ink on raised letters or ink trapped in grooves. Lithography uses a different selection mechanism: the image and its surroundings have different surface properties, so water and oily ink do not occupy them in the same way.

In traditional stone lithography, greasy drawing material marks the image on prepared limestone. Treatment establishes and preserves a contrast between image and non-image regions. The image areas accept oily printing ink, while the dampened non-image regions retain a thin film of water. That water-covered surface resists the oily ink, helping keep the background clear.

A roller can therefore pass across the whole surface while leaving ink mainly where the image belongs. Pressure brings paper into contact with the inked pattern and transfers an impression. Replenishing the water and ink allows repeated impressions from the prepared image. The selective behavior belongs to the surface and its films, not to a hidden relief carved under each drawn line.

Moisture balance and surface condition matter because they help maintain the distinction between printing and nonprinting regions. A prepared drawing alone is not the entire mechanism; preparation, dampening, inking and transfer work together. Modern lithographic printing uses related selective-surface principles, although the materials, image-making and transfer equipment may differ substantially from an artist's stone. A nearly flat surface can thus carry an image through chemistry as well as through shape.