I recently restored several VT100 that were extremely yellowed as well
as filthy dirty.
I put the plastics in my bathtub and sprayed them heavily with "Krud
Kutter", intending only to remove the dirt. To my surprise, much of
the yellowing came off too. It didn't return them to their pristine
original color but significantly reduced the yellowing as a tea colored
runoff pooled in the bottom of the tub.
https://www.rustoleum.com/product-catalog/consumer-brands/krud-kutter/clean…
I rinsed with clear water and hit them again with a soaking of the Krud
Kutter and more "tea" came off. After a third try, no more tea and so
I quit. They look really good now and I shined up the brown plastic
areas with some "Armor All" which gives it a nice shine.
I did four VT100 this way with the same results on all of them.
I don't think any of this was harsh to the plastics and so I will use
it again on other yellowed stuff.
Chris
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Chris Elmquist