Yellowing

[JaXanim]

@smiley1635

No, that's for polishing display screens. To recover original plastic surface, you need to buff away a few microns of the oxidised/yellowed surface using a polymer abrasive such as T-Cut. Any of the abrasives sold for cutting back car finishes should work. I suspect it will be very hard work to completely recover a yellowed case. Far easier to give it a respray job using an acrylic paint.
Cheers, JaX

[JaXanim]

It's clear that the plastic used for the A500/600/1200 cases is of low quality and deteriorates (goes yellow, and probably embrittles) when exposed to light for a sufficient period of time. Good grade plastics contain inhibitors to absorb the photons which would otherwise accelerate oxidation of the polymer. Any light will do. Sunlight (the most intense and includes lots of UV) causes the most rapid breakdown, but fluorescent and incandescent lights are quite capable given enough time. A candle would yellow an a1200 case given 20 or 30 years. It's all about the chemical reaction rate. The only way to prevent this is to keep the Amiga in total darkness but not in a cheap cardboard box it seems.

Cheers, JaX

[EDIT: The main culprit in the Amiga case is probably the pigment used to color the plastic. Cheap pigments simply change color when exposed to light. So the original buff color turns yellow.]