I did these with markers over the weekend and cleaned them up a bit for posting. Look at the crazy range of hues that can be squeezed out of strictly warm gray markers...the brown colored stuff is 1 and 3 warm gray Chartpak, and the purple colored stuff is 10, 30, and 50% warm gray Prismacolor. Some black and white pencil can alter the intensity of marker hue considerably.
For each design, I focused on 1. diverse shapes and curves, and 2. diverse ways to marry wood and stone. I imagined these to be the master works of the greatest axsmith in the land, somewhere around 12,000 b.c. In the comic I do for this phase of the class I'm going to invent a primitive technology where the axsmith crafts dozens of blades by firelight in his cave, then goes out the sacred tree where he embeds the blades in its branches. Over many years, the tree grows around the blades, and when sufficiently joined, the axsmith lops off the blade-containing branch and has his naturally wrought power ax.
This process is relevant to today's designed objects...materials and design elements should flow seamlessly in and out of each other.