Most of the fine scratching on a well-used pair of sunglasses was not caused by an accident. It was put there gradually, by their owner, during cleaning. The good news is that the correct method takes about thirty seconds and costs nothing.
Why dry-wiping is the problem
A lens that has been worn collects airborne grit: dust, sand, pollen, road particles. These are hard, angular and often harder than a lens coating. Wiping a dry lens does not remove that grit so much as drag it across the surface under pressure, which is a reasonable description of how you would sand something deliberately.
Each pass leaves marks too fine to see individually. A few hundred passes produce the hazy, slightly milky look that makes an otherwise good pair feel old.
The method
- Rinse first, always. Lukewarm running water for a few seconds. This floats the grit off instead of grinding it in, and it is the single step that matters most.
- Add a drop of washing-up liquid. Plain, uncreamed dish soap on your fingertips. Work it gently over both sides of each lens, the nose pads and the hinges.
- Rinse it all off. Any residue left behind will dry into streaks.
- Shake off the water, then blot dry with a clean microfibre cloth. Blot rather than scrub.
What not to use
- Your shirt. The universal habit and the worst offender. Fabric weave holds grit, and cotton is more abrasive than it feels.
- Paper towel, tissue or serviettes. Wood pulp is abrasive. Paper is designed to be cheap, not soft.
- Household glass cleaner. Many contain ammonia, which attacks lens coatings over time.
- Very hot water. Heat can lift coatings and, in extreme cases, distort a frame.
- Saliva. No cleaning power, and it dries to a film.
The habits that matter more than cleaning
Most damage happens when the glasses are not on your face.
- Use the case. Loose in a bag, a lens meets keys and coins. This is the leading cause of deep scratches.
- Set them down lenses-up. Face-down on a table is a guaranteed scuff.
- Take them off with two hands. One-handed removal pulls the frame out of alignment over time, which is why glasses drift into sitting crooked.
- Keep them out of a parked car. A closed car in South African summer gets hot enough to soften frame materials and stress the bond between a lens and its coating.
- Never push them up onto your head. It stretches the temple arms outward, and a loosened frame slides down your nose for the rest of its life.
When to accept it
Fine surface haze is cosmetic. A scratch in your central field of view is not, because your eye works to focus around it and that is genuinely tiring over a long drive. Scratches cannot be polished out of a coated lens; polishing removes the coating along with them. At that point it is a replacement rather than a repair.
