Eric works as a shading artist for Pixar. I've been around him numerous times when others have asked him to explain what "shading artist" actually means. Poor Eric struggles to describe what shading is, to onlookers who typically smile for politeness' sake, but really have no idea what he means.
How do you describe the shading on Wall*e when the way Wall*e looks shaded is the only way most people have ever seen him? It's sort of like trying to describe someone's beauty by "undescribing" that person's appearance.
Eric sometimes turns to me for support, asking me to step in with an explanation of my own. I try, but shading is really something much easier explained and understood from pictures, so I thought I'd take a crack at it from that angle.
No more talking about shading, dancing about architecture, "undescribing" beauty, etc.
On the left is a 3D model of a Cessna 172 wheel. (Airplane tires don't have treads like car tires, in case anyone wonders where the tread went.) In 3D-speak, we'd call this a model or mesh, or even just geometry. It's the structure of an object, with no other characteristics applied. (A single light was thrown in, because without a light, the "scene" would be all black.)
Even in this "clay" like state, one can easily tell the model is a wheel, because it's (more or less) geometrically correct.
But it still doesn't "feel" like a wheel.
What I mean by "feel" is this: When you look at most things, your brain enables you to imagine the way those things would feel to the touch, based on your previous experiences with the physical world. You see a piece of satin, and you can imagine how it feels. Or, you see a piece of solid steel, and you imagine it's cold and heavy. You can also avoid losing a finger, because you can mentally "feel" sharpness without having to bleed from it.
In 3D production, we add visual hints to geometry in order to help the viewer "feel" the objects with their eyes. If you can properly feel a 3D object, that object becomes more believable.
We call these hints shading.
On the right, is the same 3D object after shading. If the black portion seems like a dusty old rubber tire, and the white portion seems like dirty, oily metal, with just a touch of rust, I've done my job. If you can imagine what it would feel like to run your finger around the indented sections that form the border of the hub, all the better.
So, now, when you see a Pixar animated feature (or even one from a lesser studio), you'll know that underneath all the color, reflection, gloss, texture and grit, is a gray, featureless blob. And this is exactly how Remi, Wall*e, Nemo or any other character, car, room or cottage appears when it lands on the desk of a shading artist for the very first time.