The class project image, plus some images from my sketchbook - let's look at this technique in action - first as seen in class:

this is mostly pastel, there's very little acrylic worked into the layering, but acrylic does start off the background in a medium value of rust.

 

Again, we started with a rust underpainting, and layered from there. I'm not so thrilled with the foreground shrub, but I love the background imagery - so this is something I'd try to replicate in a larger work.