.jpg)
Score or scrape along the edges so you can split the piece with a wedge. My split wasn't totally successful, but I actually think the result got better because it ran off. It gave a stronger handle.

Start scoring the teeth.
.jpg)
The teeth should be rombic in cross section and of course have a little spacing in between. This you can achieve by scoring, splitting and abrading with a rough piece of quartzite between the teeth.
.jpg)
The handle was engraved with a stone flake. Take several turns, score first superficially, then deepen the grooves. The grooves can be highlighted with a mixture of charcoal and wax (best in my opinion) or charcoal and fat.
