Thank you all for your responses.
Michelle - I've seen your work before, and your stuff is terrific. I absolutely love the little boy with curly blond hair and an ear-to-ear grin.
Renee - thanks for the compliments. I do know what you're talking about, but I don't know specifically how to put into practice what I can't see. In my reference, and with strong light from one side - I just can't make out the darker value that turns the form. I suppose this is where you're supposed to paint what you know, rather than what you see?
If I were to do what you suggest with regards to the left cheek - at what point does the 2 steps down in value grey stop and start? Is that what blends into the background to turn the form?
The reflected light on her right cheek did jump out at me, but I figured I'd fix that when I glazed it. I thought that if the lighter value wasn't apparent in the grisaille, I wouldn't see it at all in the glaze. Again, just learning this method. I attempted to attach the reference photo earlier, and it wouldn't work - I'll try again.
John - Thank you for the kind words. I actually spent most of my morning yesterday looking at the essential Vermeer site. Twas very informative and interesting. I love the modern-day twists in Janson's work!
Lisa - Thanks for the validation. I wasn't sure if what I was doing was a no-no...but, thanks for the idea for my new series!
Yay!