How did Thomas Bewick create tonal variations in wood engraving?

Thomas Bewick, a pivotal figure in the history of wood engraving, achieved sophisticated tonal variations and textures through several innovative technical methods rather than relying on traditional cross-hatching.1

His primary techniques for creating these effects included:

• Use of Parallel Lines: Instead of cross-hatching, Bewick utilized carefully spaced parallel lines to build up a wide range of tones and textures.1
• White-Line Printing: He revived the practice of printing white lines on a dark ground by inking the surface of the relief block, allowing the artist to draw with light against the black background.1
• Lowering the Block: Bewick discovered that by physically lowering the areas of the wood block intended to form the background, those sections would receive less pressure during the printmaking process. This caused the background to print as a lighter gray, which effectively heightened the sense of atmosphere and spatial depth in his illustrations.1

By incising designs into end-grain wood with a burin, Bewick was able to produce intricate, detailed work that could be integrated directly into text blocks for efficient, high-quality book illustration.12