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Purchase a glass repair kit with cerium oxide polish in it. Use white toothpaste as an alternative to buffing compounds. Put on rubber gloves and a dust mask before using repair powder. Pour some of the cerium oxide powder into a bowl. Mix the powder with warm water to form a paste. Apply the polish with the buffing pad and an electric drill. Wipe away the excess paste with a microfiber cloth.

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Every tool you need to repair scratches comes in a repair kit. Repair kits include a polishing compound along with a buffing pad. Cerium oxide is the most common type of polish in these kits, but other products are available and work the same way.  Kits are available online or at most auto parts stores. An acrylic scratch remover is a product similar to cerium oxide. It comes in a liquid form you drip onto the buffing pad. It works best on lighter scratches. Another option is to assemble the kit components separately. Get cerium oxide or another rubbing compound. If you have a handheld buffing and polishing tool, use that to apply the polish. Toothpaste works, but it takes multiple applications to fill in scratches. Get a non-gel toothpaste with baking soda, or mix a white toothpaste with 1 teaspoon (4 g) of baking soda. Then, buff it into the scratches with a microfiber cloth or a buffing pad.  Apply the toothpaste the same way you would apply cerium oxide or another buffing compound. Wipe off the excess paste when you're done. Toothpaste has the advantage of being safer to use, but it isn't as immediately effective on most scratches. Cerium oxide powder is a pretty harsh irritant. Always put on the safety gear before opening the polish. Even if you’re careful, buffing pads tend to fling powder into the air, which will irritate your lungs.  Wearing goggles is also a good idea. It eliminates the possibility of polish splashing into your eyes. Work in a ventilated environment if possible. Open your garage door, for instance, to help disperse the powder. Keep close to an electrical outlet, though, since you need one for the buffing pad. Estimate how much of the powder you will need to fill in the scratches on your windshield. Start with a small amount, such as 2 tablespoons (14.75 g). This will usually be enough to repair a large portion of the windshield. Making the initial estimation is tricky since there are no hard and fast rules about how much polish to use. You are better off making more than you need or focusing on a single scratch at a time. As a rule, combine 1 part water for every 2 parts of powder you use. For example, use 1 tablespoon (15 mL) of water for every 2 tablespoons (14.75 g) of powder. Then, stir them together with a mixing stick to form a paste with the consistency of glue.  Thin out the mixture by adding more water, or thicken it by adding more powder. Don’t wait too long to apply the paste. If it starts to harden, spray it with more water. Attach the buffing pad to the end of the drill. Once the pad is secure, dip it into the paste or apply the paste directly to the scratched areas. Then, turn on the drill and run the edge of the pad back and forth along the scratches a few times. Keep the pad pressed firmly against the glass in order to grind the paste flat. Use only electric drills or polishing tools on the windshield. Cordless tools don’t generate enough power and may overheat. Use tools that run at 1300 rpm or higher. Remove the excess paste before it has a chance to dry. The cloth will not reach the paste inside the scratches, so you do not need to wait before wiping down the windshield. Now take some time to admire the reflection in your scratch-free windshield. If you still see scratches in the windshield, chances are the paste didn’t get inside them. Spread more paste over them. Align the edge of the buffing pad over each scratch and grind them down again.