The biggest challenge with this drawing, though, was the handling of the edges (transitions) between the light and dark passages. The secret is to make the edges generally softer rather than hard, but at the same time to keep them varied and specific. In a subject lit from a single source there will never be a single edge-quality throughout. For example, the lighting situation of this pose meant there were some fairly sharp transitions in the face and upper torso and more gradual transitions further down the figure. Even where the transitions are sharp there will, nearly always, still be a buffer area of gradated halftone in between the light and the dark. There were also a number of areas of subtle reflected light, dark ribbons of core shadow along the terminator line (between the halftones and the shadows) and passages of texture in the halftones themselves.
Of all the elements of academic drawing, transitions are probably the hardest (and usually the last) element that the student has to learn. They're also very often the difference between an average drawing and one that packs a real punch. Something for me to focus on over the coming months.