A scratch on a watch crystal can be removed by gentling rubbing it with a dab of toothpaste. Toothpaste is a very mild abrasive and will do the job easily
The tips, hints and ideas at TipKing are vetted prior to publishing however some methods remain speculative in their own nature; therefore the information should be used responsibly and at your own discretion. The Information is displayed on an "As Is" basis, without warranty. Full disclaimer