Shading and the Landmarks of Relief

<i>Shading </i>is a visual artist’s tool. It enables the indication of ‘landmarks’ inside the outline of shapes. Shading triggers behavioral responses in organisms throughout the animal kingdom and even affects the habitus of plants. Radiometry might be expected to account for the phenomenology. We derive the formal structures of shading that are expected to play a dominant role in perception. That they fail to do so suggests that shading is more of an interface template than a ‘cue’. This fits the artistic use as a ‘releaser’ very well. Pre-modern artists hardly acknowledge causal relations between various photometric variables. Their works show an effective use of various elements in their own right, with­out attempts at causal congruity. Modern art often defies physics on purpose. We identify manifest templates and relate these to conventional techniques in the visual arts.