In lesson 20 she was only shading sections which are angled away from the light, areas which are in shadow. Everywhere in shadow has the same value, no light is hitting it. At this point of the drawing we are now starting to render areas of the drawing which are not in shadow, and thus do not have the same value as those areas which are in shadow. So we aren't following that same "equal value" rule anymore. Generally there are two main things which determine how dark the value at any given spot is. These two things are (1) the angle that that spot on the surface is making with respect to the direction of the light (2) The distance of the spot from the light source. In terms of (1), the more directly the surface is facing the light, the more light that surface will catch. As the surface starts to rotate away from the light, less and less light hits the surface. If the surface is rotated at least 90 degrees from the light source, the light does not hit the surface anymore, the surface is not facing the light at all. If you rotate past 90 degrees, it doesn't get any darker or any lighter, it is facing away from the light source, therefore it doesn't get any light. As for (2), the further away from the light source the point lies, the darker the point will be. In some cases this effect is almost negligible, in other cases this effect is very severe. It depends on the scale of the object relative to the distance from the light source. For instance, if a human is being lit by sunlight, the human is very small relative to the distance away from the sun. In this case, the distance that the light has to travel to get to the human's feet is proportionally almost the same as the distance the light had to travel to get to the human's head. So the distance difference will be minimal. As another example, consider a human holding a candle at arm's length from their body. The light coming from the candle had to travel almost no distance to hit their hand. But the light had to travel a few feet to reach their face. In this case, the hand is proportionally very close to the light source compared to the face, so the hand will be much brighter than the face. I answered more than you asked for, but hopefully this all helps you and anyone else who decides to read.

I don't think I really emphasized this point enough, that just because something is "shaded" doesn't mean it's in a shadow. The shadows do have a single constant value (assuming one light source,) but the other things that are being "shaded" actually aren't shadows. The word "shaded" or the verb "shading" imply a shadow, but there really isn't one. Those darker, mid-value regions simply aren't getting as much light as the whiter regions. But they are getting some light. And it's also worth noting that even if a surface is facing the light source, it can still be in shadow if there is a different surface which is blocking the view. For instance, the ground under a tree is definitely facing upward toward the sun. Directionally, the surface should receive some light and so you'd be tempted to say that the surface will be quite bright. However, the light didn't ever actually hit the surface because it got blocked by the tree. So the shadow has higher priority than the surface angle. Which I guess I forgot to mention before because it's kinda obvious, but it's easy to forget about when you are rendering.

Parts of your subject that are closest to the light are brightest, and as the form turns away from the light they become darker until they hit the exact place where light turns to shadow. When I start laying down charcoal, it is actually an area of the light that is pretty far away from the light source. This is called midtone. It is not actually a shadow at all, but an area of the light that has some darkness to it because it is further away from the light source.

I think it's a kneaded eraser.

I believe they were done on slightly toned paper but I am not absolutely certain.

Just simply pushing the charcoal beyond the original boundary lines created by the envelope and follow-through lines by using the point of the charcoal to extend the darks.

@@thedavinciinitiative5045 I think this is a super important question. I've been struggling with my Nitram H HB B to turn the form in a satisfactory way. I've been experimenting a ton, and it seems like the H is actually good for drawing under the B and HB to fill out little white holes and also push the darker charcoal around as if one's using a tooth pick or something. Also, it appears like you may be using a purposely charcoal filled part of the kneaded eraser to do this "pushing out" of the charcoal. I've had a lot of issues with fill the charcoal paper tooth with the lighter mid tones (without resorting to brushes, stumps, swaps, etc.) and I'm wondering if that's how you're achieving that. But, yeah, I think LrnWrn has asked a very important question here :) Thanks for everything Mandy!

This is just one of many techniques for laying down charcoal. When I am doing very fine detailed work I lay it in this way, whether it is a cast or other subject.

I will look into it. Thank you for the feedback.