Leonardo's instructions for shading off a light sky will occur to any one who studies the finely gradated tints mingling with the clouds around the celestial group.
"Fra Bartolommeo"
Leader Scott (Re-Edited By Horace Shipp And Flora Kendrick)
The brush is placed firmly on the canvas and then dragged from the point lightly away, leaving a gradated tone.
"The Practice and Science Of Drawing"
Harold Speed
This method will lighten or darken a tone in varying degree, according to whether the lines are thick, thin, or gradated-somewhat in the same way that lines of shading are drawn in line work.
"The Practice and Science Of Drawing"
Harold Speed