11. Make 20 trihedral rosettes as shown, each comprised of 1 ball, 3 long reds, and 1 long yellow. Notice that the angles between the reds must all be acute, and that the yellow strut lies on the line of symmetry inside the cone spanned by the reds. This uses 20 balls, 60 long reds and 20 long yellows.

12. Attach the rosettes as shown. Each red strut from one of these rosette must attach to the vertex of one of the squat pyramids, and each yellow strut should connect to one of the trihedral vertices of the rhombic triacontahedron constructed earlier.

This is how the model should appear after you complete step 12.

13. If these 20 rosettes are connected correctly, then you should should see the vertices of a large dodecahedron, with the 12 B2 pentagons lying inside the facial planes of this dodecahedron. They are represented by the black balls in the photo. Moreover, there should be a natural way to attach 120 long blues from each of these 20 vertices to one of the vertices of the B2 pentagons constructed earlier. Moreover, attaching these should yield a total of 12 large blue regular pentagons. This uses 120 long blues.

This is how the model should appear after you complete step 13. Notice the regular compound of five cubes.