The photo above shows the picture with only black so far, in rough strokes for the first layer.
Added to the black above is some color, which will get burnished by the grey in the next stages.
This and all the following images show the burnishing of the background. This involves using a grey pencil (in this case french and warm grey both in 20%) and pushing incredibly hard onto the paper, working in tiny circular motions to blend the previous layers of color together. As necessary I add some more dark or light into the burnishing as I go.
And now on to the best part - the detailed foreground!