I start with a simple gestural sketch using charcoal. I don't concern myself with accuracy of proportions or fidelity to the source material - I'm interpreting what I see. I keep it loose to allow for any areas that may direct the course of the drawing.
Next I lay down a brushy wash of sumi ink distilled with water and applied with a bristle brush. Bristle brushes act differently than say, watercolor brushes, and this gives me the scratchy and mottled effect I like. I will smear it around with my fingers to create modeling and interesting shapes.
I now begin the process of drawing back into the image with a charcoal pencil to develop the foundation of the drawing. Whatever direction the image takes will have a solid underdrawing to work from.
The next step is to apply a combination of ink and charcoal to model the form. In some instances I will apply charcoal over wet ink to create a blurred and uneven line, or put charcoal on top of areas of dried ink to deepen the tones and create textures. Most of the modeling of the planes in the face are done by smudging charcoal around. Part of me wishes I had left it in this roughly defined state. But I'm always pushing the envelope to see if I can make it better.
Finally I tighten up the drawing by creating the landmarks of the face (eyes, nose, mouth) and laying in highlights and accents. I also play around with edges, pulling areas into sharp relief and fading other areas out-of-focus by smudging and smearing to enhance the ambiguity of the image.
That's how it works.