They are made from a single sheet of 1/4" solid walnut. Each layer is rotated a certain number of degrees from the last, depending on the design. This creates enough of an overlap for gluing. I also score lines as guides for the overlap to make assembly easier. It turns out I can glue up the whole thing in about 20 minutes in one session, as the TightBond glue grips pretty quickly. I left the edges black with no sanding (nice accent, but also much less sanding!) and then finished everything with two coats of spray Varathane. This brings out the wood grain and seals the laser charr from coming off.
One challenge was getting a piece of walnut big enough. The biggest I found was 6-8" wide strips, so I ended up butt gluing two strips together. I made a jig (shown) to insure a tight bond and one that was level at the joint. Wax paper served to control glue overflow. The joint ends up stronger than the wood itself. A few minutes with an orbital sander makes the joint seamless.
Cutting the wood took about 17 minutes for this design, but I first prototyped it in black foam board to see if I liked the shape, and to see if it was sound structurally. You can see a few other designs here.