Having spent a few frustrating hours trying to learn Blender, I was relieved to lay the blame on the Mac version of the program rather than on my ineptitude. Blender reportedly behaves on PCs, but for me, my PCs are used purely for business whilst the Macs are used solely for art. Never the twain shall meet.
Anyhow, substituting the skull project for a vase project was fine by me. I found the latter much more fun, and having achieved a glass like transparency in Photoshop, I was chuffed with the final image.
Image © PeteM2010