If I were to buy expensive sunglasses I would loose or break them but the $3 pairs I purchased years ago I still have and are in pretty good shape. Time for a change though. Decided to give them a patina’d or distressed look.
The lenses pop out the front. I rough up the plastic with a foam sanding block. Give a coat of primer. Once primer is dry I cover with a color. When color is dry I go over again with the sanding block. Pop the lenses back in and done.