...and here are 4 variations one can produce using the three materials zones (wall, roundel, and plate). I applied a simple wood texture to each zone, first the wall, then the roundel and finally the inner plate. In the lower right image, I removed the trans-mapped, rendering an inner surface flush with that of the main wall. Of course, one can apply other maps light marbled patterns, as well as reflection maps. Sincerely, Bill

Tempt the Hand of Fate and it'll give you the "finger"!