3M 6885 - Shields/Lens Covers for Full Face Respirators
3M full face masks come with one of these guys for a reason.
Once your mask is scratched, it's scratched. Little or no way to get it out without affecting the view.
If you're going to invest in a full face respirator, It would be wise to invest in protecting it. These lens covers will keep your mask's screen scratch free if rotated regularly. Fits 6800 Series 3M Respirators Small, Medium and Large