A key to controlling light is in the intersections of surfaces, and the creation of 'bones' at those intersections. As described in the glossary, a 'bone' in a surface is a localized area of increased curvature. Go back to your flexible 'highlight' mirror, and form a bone in the surface as described above. Move the surface around, and change your vantage point. You will notice that from just about any angle, that 'bend' will still be picking up highlights and consequently is well-defined. This is because unlike a flat surface, which will only pick up glare from a light at the exact right angle, the amount of curvature gathered in the narrow area of the bone will always have some part of its surface facing the light source and, in fact, probably several light sources within the environment. This allows it to always be concentrating highlights along its length. This allows a great deal of control over the graphic effect of highlights on the surface.

For example, compare a radiused cross-section to a 'boned' section covering the same area and depth. If you watch the highlights and reflections on the rounded surface, they will move up and down the surface depending on your point of view. Because the 'boned' surface concentrates most of the change in curvature to a narrow section, the essential graphic quality of the highlight is unchanged, even as the highlights crawl across the surface. Essentially you have constrained the effect within the transition from one surface to another. The tighter the bone, the stronger the highlight and the more it is constrained.

As well, the reflections have been concentrated by the localized change in surface. Instead of having one continual rounded surface where the demarcation between reflecting 'ground' and 'sky' depends on your viewpoint, the boned surface divides the section into two more shear surfaces which are distinctly oriented toward different reflections, with the bone controlling where the transition edge (or horizon line) will fall. It creates the same effect as having two planes in terms of defining the surface, but the soft transition between them allows the reflection to 'complete' itself within the curvature rather than getting truncated by a hard edge. By softening the tightness of the bone and the crown of the upper and lower surfaces, you can get the appearance of a very rounded section, if that is what you are after, while still maintaining some degree of control over your reflections and highlights.

Designing with Transitions

Once you've recognized how transition areas can be used to control the graphic appearance of your form, the next step is to incorporate it into your design thinking.

Visualize your object as a flow of graphic elements in three-dimensional space, wrapping around the various views of your object. Design your primary transitions first as a series of edges between surfaces. The surfaces necessary to create those areas of focus will naturally fall into place. Secondary transition areas will naturally occur. As a surface follows an edge around a corner, for example, the change in direction creates another transition which is likely to pick up highlights and distort your reflections. You can control the tension between those areas and your primary transition areas by balancing the tightness of them. The tighter the transition, the stronger the highlights will read, creating a hierarchy of compositional elements in your three-dimensional form.

You can control the amount of 'movement' over surfaces and the contrast between adjacent surfaces by adjusting the amount of crown in each surface and therefore the steepness of the transition between them. Keep in mind that it doesn't take a great change in the angle of a surface before it picks up a significantly different character of light and reflection from the world around it. Then you can control the softness of the transition by increasing or decreasing the tightness of the bone, or choosing to use an edge, radius or a bevel.

In the end, the primary character of your design will be consistent regardless of the view or viewing conditions. You will be able to control the graphic flow of your forms, as well as how and where reflections and highlights fall across your surfaces to define their shapes.