I also remember so vividly the classes in my college drawing classes where "Miss Ruby" had us do the same, but she put together a still-life composition using black and white patterned fabrics and tossed in a small stool and a philodendron. I learned so much from that exercise, in negative space, flowing shadows, and just using light and dark to express what we saw. Only charcoal and white paper.
On another occasion, she wadded up a large brown paper grocery bag (1970-ish), and had us express it in India ink washes on white paper.
In both of these exercises, we were not allowed to draw any lines. We could only use shapes of light and dark.
I have used those two techniques more than any other thing I ever leaned in college, and by many many orders of magnitude.