Watch the Light to Light the Watch.

For those wanting to get an idea of just how well you can control specular highlights, I recommend viewing Strobist reader Ming Thein's gallery of watch photographs.

A watch is a tidy little nightmare of complex, reflective surfaces. Specular highlight control is pretty much all you have to work with.

One of Ming's go-to techniques is to shoot a tightly zoomed beam of light through a larger diffuser. He is using the reflection of the edge of the light hitting the diffuser (might want to stop and think about that one) to get lovely edges to his highlights.

Put differently, the light from the flash is not "filling" the diffusion material. The edge, where the light softly ends, is reflected in the watch - just where Ming wants it to be.

Simple technique, elegant light.