A fun fact about art method evolution is that it's tied to material science quite a lot, but people like to ignore that fact very much. For example, let's take how they drew faces in the 20th century with the Loomis method or the Asaro head and compare it to what the Renaissance masters did, particularly Leonardo.
Loomis, in his book, describes a proportion guide and a simple guide to the "planes" of the face, which the Asaro head gives a more detailed model of. The planes, in this case, are a simplification of the actually round nature of the human face to divide values easier. Think of it like peeling a potato. The bigger cuts you make with your peeler, the blockier it becomes, but in this case, you are doing it to later round it back out. Important to note that even the proportion guide, which doesn't quite touch the planes of the face on first glance, starts off by chopping off the sides of a sphere, thus giving you at least two flat planes of the face, which we later draw to be the temples.
Now, how Leonardo did it. First, an apprentice was taught how to draw the features of the face individually. Think of those old YouTube tutorials that taught you how to draw a perfect eye or lips, but during 15th century Italy. Then, that knowledge was applied to a proportion guide, an egg. Yes, a literal EGG. They would take an egg, which they thought roughly resembled the human head without the neck, divide it with a vertical centre line, brow line, nose line and chin line, thus getting the thirds of the face, and place the already-taught features onto this guide. Then, they would slowly hatch the drawing to create shadows.
So, where does material science figure into this? Starting with the drawing, there is a huge culture shift. Graphite pencils weren't a thing in Leonardo's time, and charcoal was not considered stable enough, or controlled enough, to be used in drawings that mattered, only for cartoons (not animation, the disposable drawings that would be used to transfer sketches to canvas or walls). Thus, silverpoint was used. Silverpoint cannot be erased, however, so the slow buildup of shadows became paramount. You couldn't just "rough in" shadows and erase them later to form a more cohesive piece. Loomis, however, had graphite and more stable charcoal and four hundred years of art evolution that gave him a proper eraser and stable surfaces that allowed for a quick distribution of values, which had become the mainstream approach in painting too.
What was up with painting? The same thing! Leonardo, to paint a portrait, had to do three layers of underpainting to decide where he was placing any given shadow and then slowly build up an underpainting in oils that built up shadows. The pigments they used for painting didn't have enough staining power, in most cases, to cover the canvas well enough in one smooth motion, like they would come to do later, so slow buildup was necessary. Now, when you are slowly building up a brown and white underpainting that you will inevitably glaze over, instead of refining in any major way, you don't want to "rough in" shadows. You want everything to be smooth already. And what's naturally always smooth and resembles the tone of human skin? An egg, that's right. Now look how paintings were done in the French Academic school and are done today. You do a rough sketch or a rough underpainting, most likely without even major shadows being painted in, and then paint the general shadow and the general light, the two averages of the portrait, since your paints can do that quite easily now. Then, you start carving out the half tones between those two, adding features, working this painting to an amazing finish (or not, I won't judge). This approach needs good knowledge of the planes, since they are the main factors in how these rough values are distributed. A good example of it is how the upper lip is always darker than the bottom lip. That is because the downward angle of it makes it catch shadows. Thus, methods like the Loomis method or its predecessors became popular.
People love to rage about not being taught art history and only being taught about wars and other such stuff in school. The truth is, war shapes art. The pigment strength that allowed this evolution and ease of painting is due to wars and trade. It is not the knowledge of either you lack, but the ability to relate one to the other.
Anyway, I am off to suffer through another session of charcoal drawing.
