Tonal bars (2B pencil and technical pen)
Keys to Drawing, Chapter 2, Project 2D. Make a Tonal Bar
Procreate on iPad Pro 9.7"
Exercise: Make a 1.5x8" panel and create within it an evenly graded tone from black to white. Use a soft pencil and build up the tone deliberately and patiently, squnting from time to time to check your progress. Strive for a smooth transition between tones and watch for "spots" of light or dark. The middle tone (50% black) should be in the center of your bar. Allow yourself 30 mintues.
If you are interested in pen and ink, try a second tonal bar using the crosshatch method. The tones will be slightly coarser than your pencil version, but when you step back, the overall effect should be the same. To create the light areas, the pen strokes must become gradually less numerous and farther apart. You may want to use the examples shown here as a general guide for both bars.