According to the text at the top of:
http://alatest.com/reviews/laptop-reviews/apple-ibook-g4/po3-1379,30/
the case is made of polycarbonate.
Polycarbonate is a tough plastic, but its kyrponite is ammonia.
I once spent a lot of time polishing the mold marks from a G4 Cube case with Meguiars plastic polish. The result was a case that was better than a new one. The Cube had to be sent back to Apple for a repair. I enclosed a letter asking them to be careful with the case. I got back a computer with a new case, with mold lines, and a form letter stating that all components of my G4 Cube had been updated to current specifications.
