The images was them V-carved into a piece of black Komatex (a foamed PVC similar to Sintra) using a 60 degree V-bit. The material was held fast to the spoilboard with a high-bond acrylic tape from a company called Nitto-Denko. (It is a low VOC tape that we have around because it can be object-friendly in our museum exhibits in many cases.)
The figure on the lower left is not a centaur - it is our dog Marlowe, damn it - open your eyes. Mom, Fletcher and Chloe round out the tableau. Dad must be working on the robot.