Fixing sun yellowed clear plastic?

[57peppershaker]

A buddy has just picked up a 55 Chevy diecast thats been in the sun for too long and all the clear plastic windows & lights have yellowed pretty bad.

Any was to fix it ?

[Snake45]

Is the clear plastic injection-molded or vacuum-formed? 

[Mark]

I've never seen vacuform clear parts on a diecast, but the plastic used for windows is a lot more flexible than what is used in kits.  The diecast body won't flex, so the windows have to, otherwise they wouldn't go in.  You can try polishing the clear parts, but I'd bet there is little chance of undoing the yellowing.  You might be able to get rid of some of it though.

[Snake45]

3 minutes ago, Mark said:

I've never seen vacuform clear parts on a diecast, 

I haven't either, but then I don't think I've ever seen injection-molded clear plastic go yellow. Had to ask. 

Yellowing of some types of clear vac-plastic is a well-known phenomenon in Model Airplane World. Many have tried many things, but so far no one's found a cure. 

[Snake45]

Was just googling and came across this. Never heard of it before. Worth a try, maybe: 

https://pinside.com/pinball/forum/topic/say-goodbye-to-old-yellowed-plastics

[Mark]

Thinking about it, I wonder if one of those cleaners for yellowed car headlamp lenses might do the job.

[62SY4]

5 minutes ago, Mark said:

Thinking about it, I wonder if one of those cleaners for yellowed car headlamp lenses might do the job.

Every headlamp restoration kit I have ever seen is just some type abrasive compound. Really expensive for the volume you receive. 

I was thinking along these lines though, might be worth trying some fine or finishing compound. 

[peteski]

If the yellowing is only on the surface then the abrasive/polishing method will remove it. But if the entire material is yellowed, I don't think there is anything that can be used to make it clear again (other than maybe using the yellowed part as a buck to vacu-from a new windshield from clear plastic).

[Tom Geiger]

Not thinking about it lately but back when people first started using 90% alcohol for paint stripping, I put a kit glass shot that had some brush paint on it into the drink.

I was surprise that not only did it remove the paint, but the yellowing was gone!  Maybe try it.