Using a pencil, divide the space into the number of bands required. Work a split stitch outline.
Starting in the centre of the shape, work the first satin stitch band of colour over the split stitch outline. The depth of the satin stitch should be one third deeper in height than you wish to be seen.
Using another colour or shade, work another row. Start each stitch at the bottom and take the needle down splitting the stitches above, covering one third of the band above.
Structure of stitch
Identifying Block shading
Similar in technique to long and short stitch and satin stitch, block shading stitch is instead rows of satin stitch worked in line so each stitch is next to the other, encroaching at a similar depth into the first row of satin stitch, and in the same direction as the first row.
Jacqui McDonald, RSN Essential Stitch Guides: Crewelwork (2010)