Engraving on marble with cnc works very well:
(Wedding present. Her favorite animals are pygmy hippos. He proposed at the zoo in front of their enclosure)
Artwork created in Affinity Designer. Saved as png and then imported to Fusion 360 with image2stl. Pocket tool path 1.5mm tungsten carbide ball end. 400mm/m with .2 step-down total. (set heights in Fusion for top to be model top and bottom to be model top -.2mm) Operation repeated several times with z-origin lowered .2mm each time until I got depth I wanted. I leveled wasteboard with 1" surfacing bit beforehand but even so between bed and stone not being perfectly flat (slightly convex) I’ve found it works best to just carve one height and repeat as necessary.
-S