The model was made using Rhinoceros® capabilities in terms of NURBS editing, the weight of NURBS control points was set according to an increasing intensity in one dimension logic. The other dimension of the matrix was used to merge two different actions (gather and cut for example).
The milling was made using a tile of Styrofoam®, the milling process was organized in 3 different phases (one roughing the surface, the other two refining it).
Final result from the top.
Some parts of the surface had been sanded to a smooth surface whereas other parts were left with the original finished texture.
Perspective view of the final result.