A long-forgotten pad of Art Paper in assorted colors came to the surface:
An angled view shows off the layering a little better:
Done manually with LightBurn’s Offset tool: shrink the frame’s interior openings (which lie outside the frame) by 1 mm per step, then cut each shape into a different color. The black layer is a complete disk, stuck atop a plain chipboard disk for stiffening.
In the cold light of day, I think I offset the green layer by 2 mm.
It’s not a particularly useful coaster, because you want a flat surface under your drink, but it does look pretty. Nowhere close to that good, but I like it.
The next time around, I’ll automate the process by stepping the sash width by 1 mm and saving each SVG image separately.