In the past I have used a similar technique to paint this Space Wolf Logan Grimnar. The miniature was first spray painted Chaos Black and then when dry the figure was spray painted Skull White from directly above the figure, 'the hallo effect', which leaves the miniature with ready made shadow and highlighting effects. When you paint the miniature the highlighted areas show brighter and the black areas are already in shadow. Once again I would hope the figure would show the technique better than words - maybe a photo tutorial would be better!
In model aircraft forums or articles the technique is called 'Pre-Shading'. I will continue the robot On-Line build with a simple Black/Brown Wash, see next Blog entry.