Use a soft cloth that isn't abrasive. Paper towels are notoriously abrasive. If you're gentle, a soft kleenex will work. Windex probably is overkill, instead use isopropyl alcohol.

I used to work at a jewelry store, and we used something called a "Selvyt" to wipe fingerprints off of the jewelry. I kept one, and I keep it in the car to clean my sunglasses with. I also use it to wipe fingerprints off the face of the empeg when I'm in the car.

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Tony Fabris