I planed and jointed 2 × 12" dimensional lumber (spruce I think) into a large blank, laser etched it on both sides and cut it out with the router. Final size is 5 feet wide. I finished it with many coats of spar urethane.
At least 24h per side of lasering. I did a lot of tests to find optimal settings. I use ESTLcam by pocketing as a 0.2 mm wide tool at 80% intensity and 1000 mm/min.