Abstract
In European painting, “illusionism” was one of the dominant aims since the 15th century. Some means to achieve it have been well studied and described, e.g., the application of perspective, or of shadows and shading. Much less attention has been paid to the handling of paint itself. Subtle manipulations of paint and paint-layers to achieve particular effects of convincingness were a form of incorporated knowledge, hard to describe in instructive texts for painters. Yet, every now and then we encounter remarks about paint handling as a way to capture or render certain optical effects. In several older treatises this concerned contours or edges of painted objects. For example, Willem Goeree (1668) argued that in nature there are no contours created by lines. In drawings one has of course to work with lines, but is better for liveliness and convincingness, he says, to omit these sometimes. This is especially important for parts of objects that receive full (day-) light. The effect referred to here in drawing, was also used in painting, where contours were sometimes purposely made vague by blending and smudging the paint. It may be argued that such blending does not really occur in nature, just like its opposite, a distinct linear contour around objects. Yet, there are plenty examples of artists using contour vagueness, but also contour enhancement, although there is no quantitative data about its usage, nor its perceptual effects. To understand the effect of contour style, we conducted an experiment using a rendered 3D shape and manipulated the contour by adding a black line, or by blurring the edge. Indeed, local slant settings were diminished (i.e., flatter) when a contour was added. However, blurring did not increase three-dimensionality. Perhaps the abstractness of a controlled experiment contributed to the lack of effect.