This is an Art-O-Graph, although I've always known it as a "Lucy." I suppose this moniker is derived from camera lucida. I found it in the back of a junk closet at school, along with an waxing machine and other artifacts of the predigital era of Design Arts. At least once a year I have to keep someone from hauling it away as garbage. It works a like an inverted opaque projector: you put an image in a lit chamber above a pair of sliding lenses; then, you adjust the lenses until the image is projected at the size and clarity you want on the table below. In this instance, I stuck my original pencil drawing in the chamber, and projected it onto a block of Arches 140 lb. Cold-press watercolor paper.
This is the tracing of the projected drawing, darkened via Photoshop for your ease of viewing. The idea is to actually have a very light drawing, so that it won't show through the paint.
If I were at home, I might have just redrawn the sketch at a larger size by hand, or blown it up on a xerox machine and traced it with my shoestring light box (a pane of glass balanced on my lap and a desk lamp between my feet). Or made the xerox into a sheet of carbon paper by rubbing the back with graphite and transfering it.
And then I restablished my line drawing with a thin painted line, and blocked in the basic value scheme. The paint I'm using is about half Prussian Blue and half Payne's Gray. I think I meant to just use Payne's Gray, but grabbed the Prussian Blue by accident, and thought Huh, okay. At this stage, the color doesn't matter as much as the value.