Studies from Sittings...

Human models asked to sit for portrait studies either are friends and acquaintances or are hired professional models.
From my experience the hired model will endure longer sitting lengths than friends do. As well, professionals are so used to being looked at intensely for extended perions of time that of expression to take over their they tend to relax into poses to the point of allowing a range of expression in their visage as they sit, quite unselfconscious.
Friends and family, on the other hand, tend to pose, to present their best face - their "game face" - unless they don't invest greatly in the outcome, the resulting study.
One cannot let the expectations of the model influence the action of seeing, studying and responding to a particular human face or form. If the one drawing is not able to fully engage in the act of seeing and drawing, then the freedom with which to make marks is compromised.
This drawing of a young woman model allowed me enough comfort to "attack" the drawing with vigour and to use charcoal in a direct manner. 18in. by 24in. compressed charcoal on cartridge.