Painting and drawing with the Art Media tools : Using the Smear tool
 
Using the Smear tool
The Smear tool lets you smear existing pigment, including pigment that has no volume on the canvas, such as pencil strokes. The tool simulates the effects of dragging a cloth or finger through chalk or pencil strokes on a canvas.
You can use the Smear tool to create a smudging effect on dry pigment, or to create a smearing effect on wet pigment.
Smear tool options
Edit workspace 
Smear tool options include
Shape — defines the shape of the tool tip
Size — defines the size of the tool head in pixels
Thickness — defines the aspect ratio of the tool head
Rotation — defines the angle of head rotation in degrees
Head Tracking — controls whether the tool head bends around the path of the stroke, or whether it remains at a fixed angle