Road film, oil, tar, grease, water spots and more bonds to glass and are difficult to remove. Windshields and especially the rear window on trucks and SUVs are exposed to harsh conditions. Run your fingers over the glass. If it doesn't feel as slick as ice, it needs claying. Eliminate heavy road film, tar, bug jerky and even water spots quickly and easily. Glass Cleaning Clay is the perfect glass prep before polishing. Clay also works on a variety of smooth, hard surfaces such as glass shower doors, chrome, stone, ceramic tiles, synthetic stone and quartz surfaces. Removes water spots from windows around your home. Always use a proper lubricant when cleaning with clay. We recommend Griot's Garage Speed Shine® as a lubricant and Speed Shine® Micro Fiber Cloths. 3.5 ounce, 100-gram bar. Finish up with Griot's Garage Window Cleaner and Micro Fiber Window Cloths.