Hi Pilou,

> How do you find the good proportions of the
> polygons from the triangle?

I believe any proportion you pick will still make a solid, the proportion you choose will just control the proportions of the pieces in the solid.

For example here with larger triangles and smaller "truncated" spots:



That makes a solid like this:




I guess this is similar to a Truncated tetrahedron:
http://en.wikipedia.org/wiki/Truncated_tetrahedron

- Michael