I have used the Retrobrite method on different kinds of playfield plastics.
It worked best on a '70s Gottlieb EM pop cap, turned it from yellowed to a perfect white. I was amazed.

On white playfield posts and guides it works quite well, certainly taking the yellow out and ending up with an ivory color, which might be the original tone anyway. It definitely super cleaned them at the least.

I haven't had any luck with color posts, some plastic acted funky and got sticky.

I used the solution in a zip-lock placed into a small plastic tub. Left it in the sunlight on a windowsill for a couple of days.

I ended up using the stronger H2O2 from beauty supply shops rather than the weaker solution in drug stores. But either works, just takes longer.

It seems that the Retrobrite method works best on hard plastic, and quite well on softer plastic like posts.

Care must be taken with handling the stronger H2O2, I don't know how people put that stuff on their head for hair coloring!

Alan

These caps had most of the printing already gone. What little was left didn't disappear after Retrobrite but it appeared to be a bit more faded. More experiments are needed for printed parts.

Here are photos before and after.

popcap1.jpg

postwht1.jpg