I wanted to make a "white silhouette" of an egg on a medium background. My backgrounds were all pretty blotchy, so I used a Woodman's bag and white pencil.
This egg stuff was to be a practice of soft (or blended) edges on a curved surface. On this drawing I tried to show these kinds of edges: Hard Edges, Soft Edges, Found Edges, and Lost Edges; plus these aspects of shading: Highlight (only on boiled eggs), Body Tone, Shade, Reflected Light, and Cast Shadow. My favorite is "lost edges." Subtle stuff, easy to miss because your eye fills in the line.