Clay Brush
From ZBrush Info
The primary purpose of the Clay brush is to sculpt surfaces using alphas. While the other brushes may be used to do this, they can have side effects that come about as a result of their 'main' purpose. The clay brush is intended specifically for sculpting with alphas, and will not cause other side effects.
The Z Intensity and Clay slider values together affect the result of sculpting with the clay brush. See below.
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Controls
Clay: The Clay brush is a general purpose brush for sculpting with alphas. The clay slider scales the alpha as a whole; this affects not only the intensity of the sculpt, but also the size (width and height) of the brush stroke. The standard Z Intensity control affects the magnitude of the alpha up/down displacement effect, but does not affect the size of the alpha.
In the image to the left, the Z Intensity settings (which differ horizontally across the image) affect only the 'bumpiness' of the sculpt. The Clay settings (differing vertically across the image) affect the 'size' of the sculpt. These two combine to determine the total displacement along the surface normal of the sculpt.
