My father sculpts and paints eggs (here, it's a Emu's egg http://en.wikipedia.org/wiki/Emu) with a Dremel rotary tool and acrylic paint.

In February 2008, I ask my father to paint a tiger for me, because he has very little free time, it took a year an a half to complete it.

Here's as it was in august 2008, a year ago. The green behind the tiger is the actual shell of the egg, polished to reveal the pale sub-layers. Emu's eggs are dark green and the white region has been created by sanding two thirds of the shell's thickness. More you remove, whiter it become.