Not sure why this has never occurred to me before, but I had a genius idea tonight and thought I'd share it in case it helps anyone else.

As I was sorting some kit, I was just about to throw away an old diving pressure gauge that's so scratched that it is impossible to read the numbers. I lent back on my heels to stand up, and my eyes fell upon a pot of T-cut on the shelf. Worth a shot, I thought.

Well, after a few minutes work, the lens on the gauge looked like new! I can even read the numbers without my glasses now!

Next on my list was a rather scratched old Petzl Duo. I always used to say that the cheapest upgrade for a Duo was a new lens; it doubles the brightness straight away and only costs a few pounds. But it turns out that T-cut will restore a scratched Duo lens in minutes too, saving a few quid and a bit of landfill.

I'm no chemist, but I'm pretty sure that this will work for most clear plastic lenses. It's probably a good idea to use the neutral colour though, unless you want some funky lighting effects! 

Brasso would probably work as well.

Says a lot about the Duo.

There's a thing called Polywatch that works well too on plastic (not glass) watch faces that I've used with general success.  https://www.amazon.co.uk/polyWatch-Scratch-Remover-Repair-Polish/dp/B00E3T237C  (other vendors are available).  Autoglym works as well - used it on a plastic torch lens.

I have in the past used T-cut on car headlamp lenses and UPVC window frames. Also with great success on a white toilet seat cover that a cleaner had poured  neat bleach or some other aggressive cleaning product over leaving a matt finish in the shape that the chemical first touched the lid. A little elbow grease and T-cut and the lid was back to a glossy shine.

Other very fine abrasives I've heard it said work well too, like toothpaste.

When servicing forklift trucks we used to polish the perspex screens with a silicone "cockpit" spray, it surprisingly seemed to bring back relatively clear visibility to badly scratched screens. I guess the silicone filled the finer scratches. The silicone spray is the sort of thing car dealers use to clean and shine the cars interior plastic & vinyl trim (often a little too enthusiastically in my view).

Maj.

If scratches are too deep for a fine abrasive to work, and you're on the verge of throwing whatever-it-is away, a coating of clear nail varnish is worth a try.Not perfect, but considerable improvement.

I've had mileage out of creme cleaner and toothpaste in a similar manner to this.
Maybe useful if you don't have T-Cut lying around?

I've tried both toothpaste and Brasso to polish out some fine scratches in clear acrylic tube.  I'll give the T-cut a go.  As a last resort I'll try exposing it to acetone vapour.

Silicone spray is good for getting a final cut on hard plastic to a good finish on the lathe.

There's a product specially developed to polish car headlights called "K2 Lamp Doctor" available online for about 4 quid a tube. There are also a few ceramic coatings that claim to give a 9H hardness to plastic headlights, some of these work if they are cured properly.

This is great, I've been looking for a way to polish the face of my cheap Casio watch which has a fine haze of scratches. I wondered about T-cut but Polywatch sounds better!