Simultaneously plastic and determined

Pastel and charcoal on paper
18" x 24"
Untitled Study

I'm hoping I can build from this and make a line of pictures which will help me refine the technique and style of overlaying light and dark to build shape.
While working on my shells series over the last weeks I've become attracted to the subtleties of what I think I should describe as tone.  By that I mean very close shades of color which when placed next to each other can reveal depth.  Also I think subtle color variations don't just have a visual impact in the sense of perspective; they also reveal aspects of the subject  beyond the structure of the image........or maybe I'm over thinking it! Ha!    
Anyway, when I look at this I see flexibility and strength in some tension and I like that revelation.