Mineral glass is tempered glass. Made from silica, it is commonly used for watch crystals, as it is scratch-resistant. Mineral-glass crystals can get cloudy and dirty over time, because of exposure to debris, dirt, oil and other environmental factors. To clean a mineral-glass crystal, follow some simple steps.

Dampen a soft, clean cloth with rubbing alcohol, and gently wipe the face watch in a circular motion.

Place a pea-sized amount of ordinary toothpaste on an old toothbrush or another small, soft-bristled brush.

In a circular motion, gently rub the toothpaste on the watch crystal. Do not brush too hard, as the mineral glass is scratch-resistant but not impervious to scratches.

Dampen a new clean cloth with water, and wipe away the toothpaste.

Use a new clean cloth to gently dry the watch face.