The honest-char rule from the essays has a limit, and this attempt found it. On wood the dark edge reads as a finish. On pale veg-tan it wandered — the cut line charred and the burn crept sideways into the grain like a coffee ring.
One pass at cutting power was too hot for the hide. The engrave face was fine; it was the cut-through on the wallet outline that scorched. Masking tape on the top face helped the surface and did nothing for the edge.
Marked failed and kept on the reference shelf. Next attempt goes down in power and up in passes, and cuts from the flesh side. The leather gets a say, same as the wood does.