Good morning Katherine!
Another great drawing underway I see. Please call me Anthony and never worry about how busy I am. I genuinely love talking shop and make a good effort to get to all the content presented to me (although sometimes it may take a bit. LOL!) Also, I am sorry to learn that there has been some negativity encountered within your current course. I do hope though that you can still get some productive development out of it.
Your own assessment and observations here are quite astute. I am probably going to sound like a broken record after the last drawing you shared, but if your goal is to capture the communication of form found in the provided reference then you will need to venture into much darker values.
First, remember to keep in mind that our perception of lightness or brightness values is demonstrably contextual. Look at this example that I use quite often:
This image of stacked cubes contains a useful truth in that all the illustrated cubes (A-D) are identical in lightness value. A=B=C=D and a=b=c=d. However the values of the surrounding context lead us to a perception of cubes that are very different. I share this to try and emphasize just how important context is.
As such, I would highly recommend starting with solid anchors. If I haven’t mentioned anchors before, they are values or colors assumed to be “true”, usually due to observation as well as a material limit. For example, the darkest dark I can observe might be linked to the darkest color or value I can create. This way, a material limit is contributing to the identity of the anchor as opposed to just another (strictly) perceptual judgement. Other anchors might be the lightest lights, or in the case of a colored materials–the highest chroma color observed. With these anchors established you can make judgments that are far more useful when your goal is to replicate perceived relationships in a subject. In other words, anchors are like “:givens” in an algebra problem like 2x=4. It is rather easy to solve for x here because we are provided with the given variables. The 2 and 4 in this context would be metaphorically analogous to perhaps a darkest dark and your lightest light. With those established you can far more easily solve for x.
Some possible dark anchors here might be a swatch of the hair that is darkest on the reference or perhaps even the pupil (which, as a void, is often one of the darkest darks in a portrait image.) But look how far your drawn pupil value is from the anchor pupil I moved close to the eye in your drawing. With these two possible anchors added you can easily see how light-shifted the value structure actually is.
I’ve also added a sample strip (labeled A) on top of your drawing from the reference just so you can see and better appreciate just how far the dark has to go. Samples B and C come from the white paper you are drawing on which is also serving as a strong contextual influence during drawing development. Placing your blank paper samples onto the reference face and background (again B and C) allows you to see just how much the white paper may be influencing your judgements (remember the image above. All those cubes are identical in value—but the context is different.)
I know that it can be scary to get dark in a drawing or painting. It brings with it a sense of irreversible commitment that can really keep the more timid and less-experienced at bay. However, behind that membrane of fear and hesitation is a vast landscape of successful representation. You just have to be willing to push through it!
Hope this helps and hope you keep us posted!