How to Fix a Scratch on Glass: Windows, Mirrors, and Glass Surfaces

Glass scratches are one of the more challenging home repairs — glass is hard, transparent, and unforgiving of mistakes. But most surface scratches on glass are repairable at home using cerium oxide, a rare earth polishing compound that's been used by glass professionals for decades. The process requires patience and the right technique, but the results can be dramatic: scratches that were clearly visible become nearly invisible after polishing.

This guide covers scratch repair for windows, mirrors, glass tabletops, and other glass surfaces, including an honest assessment of which scratches are repairable and which aren't.

Can Your Scratch Be Repaired? The Fingernail Test

Before investing time in glass scratch repair, assess whether the scratch is repairable:

Run your fingernail across the scratch.

• Fingernail doesn't catch — The scratch is very shallow, in the surface only. Highly repairable with cerium oxide polishing. Excellent results expected.
• Fingernail catches slightly — Moderate scratch. Repairable with cerium oxide, but may require more time and effort. Good results expected with patience.
• Fingernail catches noticeably — Deep scratch. Partially repairable — polishing will reduce visibility significantly but may not eliminate the scratch completely. Manage expectations.
• Fingernail catches deeply, scratch has visible depth — Very deep scratch or gouge. Not practically repairable at home. Glass replacement is the better option.

The honest truth about glass scratch repair: polishing works by removing a very thin layer of glass around the scratch to level the surface. This makes the scratch less visible but doesn't fill it. Very deep scratches require removing so much glass that the optical distortion from the polished area becomes a problem. For deep scratches, replacement is often the better long-term solution.

Special Considerations by Glass Type

• Tempered glass — Used in shower doors, some windows, and glass tabletops. Can be polished for surface scratches, but be aware that aggressive polishing can weaken tempered glass by removing the compressed surface layer. Work carefully and don't over-polish.
• Laminated glass (safety glass) — Used in car windshields and some windows. Has a plastic interlayer between two glass layers. Surface scratches on the outer glass layer can be polished. Scratches on the inner surface (inside the car) are not reachable for polishing.
• Coated glass — Low-E windows, anti-reflective glass, and some mirror coatings have special coatings that can be damaged by polishing. Check with the manufacturer before polishing coated glass.
• Mirrors — Mirror scratches are on the reflective backing, not the glass surface. Polishing the glass surface won't repair a mirror scratch. Mirror scratch repair requires touching up the reflective backing from behind, which is complex and often not practical.

What You'll Need

• Cerium oxide glass polishing kit — The Cerium Oxide Glass Polishing Kit includes cerium oxide powder, a felt polishing pad, and instructions. Cerium oxide is the professional standard for glass scratch removal — it's a mild abrasive that polishes glass at the molecular level, removing the scratch by leveling the surrounding glass surface.
• Drill or rotary tool — For attaching the felt polishing pad and generating the speed needed for effective glass polishing. A variable-speed drill works well.
• Spray bottle with water — Cerium oxide must be kept wet during polishing. Dry polishing generates heat that can crack the glass.
• Masking tape — To protect the surrounding area from cerium oxide slurry.
• Microfiber cloths — For cleaning the glass before and after polishing.

Step-by-Step: Polishing Out a Glass Scratch with Cerium Oxide

Step 1: Clean the glass thoroughly.
Clean the scratched area with glass cleaner and a microfiber cloth. Remove all dirt, grease, and residue. The glass must be completely clean before polishing — any grit on the surface will create new scratches during polishing.

Step 2: Mask the surrounding area.
Apply masking tape around the scratched area to protect the surrounding glass and frame from cerium oxide slurry. Cerium oxide is a fine powder that spreads during polishing and can be difficult to clean from window frames, sills, and surrounding surfaces.

Step 3: Mix the cerium oxide slurry.
Mix cerium oxide powder with water to form a slurry with the consistency of thin paint. The exact ratio varies by product — follow the instructions in your kit. The slurry should be fluid enough to spread easily but thick enough to stay on the polishing pad.

Step 4: Apply slurry to the felt pad.
Apply a generous amount of cerium oxide slurry to the felt polishing pad. Attach the pad to your drill.

Step 5: Polish with overlapping circular motions.
Set the drill to medium speed (1000–1500 RPM). Apply the spinning pad to the scratched area and work in overlapping circular motions, covering an area about 3–4 times larger than the scratch itself. Apply moderate, consistent pressure. Keep the pad moving — don't hold it in one spot, which generates heat and can crack the glass.

Step 6: Keep the surface wet.
Spray water on the glass every 30–60 seconds to keep the cerium oxide slurry wet. Dry polishing generates heat that can crack glass, especially tempered glass. If the slurry starts to dry and turn white, add more water immediately.

Step 7: Check progress frequently.
Stop every 2–3 minutes to wipe away the slurry with a damp cloth and inspect the scratch. Glass polishing is slow — don't expect the scratch to disappear in one pass. Check progress and continue polishing until the scratch is no longer visible or has been reduced to an acceptable level.

Step 8: Clean thoroughly.
Once the scratch is repaired to your satisfaction, clean the glass thoroughly with glass cleaner and a microfiber cloth. Remove all cerium oxide residue — dried cerium oxide leaves a white haze that's difficult to remove if left to dry completely.

Step 9: Inspect in different light conditions.
Inspect the repair in direct light, raking light, and from different angles. Glass scratches are most visible in raking light. A successful repair will be nearly invisible in all light conditions.

Alternative: Toothpaste for Very Fine Scratches

For very fine surface scratches that barely catch your fingernail, non-gel white toothpaste can reduce visibility. Toothpaste contains mild abrasives (similar to very fine polishing compound) that can polish out extremely shallow glass scratches.

Apply a small amount of white toothpaste to a damp microfiber cloth and rub in circular motions over the scratch for 1–2 minutes. Wipe clean and inspect. This method is much less effective than cerium oxide but requires no special equipment and is worth trying for very minor scratches before investing in a polishing kit.

Window Scratch Repair: Special Considerations

• Work from the outside. Most window scratches are on the exterior surface. Access from outside gives you better control and prevents cerium oxide from getting inside the house.
• Protect the window frame. Cerium oxide slurry will stain wood and aluminum frames. Mask thoroughly before starting.
• Double-pane windows. If the scratch is on the interior surface of a double-pane window (between the panes), it's not accessible for polishing. The window unit needs to be replaced.
• Check for Low-E coating. Low-E windows have a metallic coating that can be damaged by polishing. Check with the manufacturer before polishing any window with a special coating.

Glass Tabletop Scratch Repair

Glass tabletop scratches are among the most satisfying to repair because the glass is accessible from above and the results are immediately visible. The cerium oxide method works well on glass tabletops. A few specific tips:

• Remove the glass from the table frame if possible for easier access and to protect the frame from slurry.
• Work on a padded surface to prevent the glass from sliding during polishing.
• For tempered glass tabletops, use lighter pressure and shorter polishing sessions to avoid over-polishing.

Frequently Asked Questions

How long does glass scratch polishing take?
For a light scratch, 5–10 minutes of polishing is often sufficient. For moderate scratches, plan for 20–30 minutes. For deep scratches, polishing may take an hour or more and may not fully eliminate the scratch. Patience is the most important ingredient.

Will polishing create optical distortion?
Light polishing of a small area creates minimal distortion. Aggressive polishing of a large area can create a slight optical distortion (a wavy appearance) because you're removing glass unevenly. Work the polishing pad over an area larger than the scratch to minimize this effect.

Can I fix a scratch on my car windshield?
Yes, for surface scratches on the outer glass. The cerium oxide method works on windshields. However, be aware that windshields have a plastic interlayer — scratches on the inner surface (inside the car) are on the glass surface facing the interior and can be polished from inside. Deep scratches that affect visibility or structural integrity should be repaired by a professional.

Can I repair a scratched mirror?
Mirror scratches are typically on the reflective backing (silver or aluminum coating on the back of the glass), not on the glass surface itself. Polishing the front glass surface won't repair a mirror scratch. Small mirror scratches can sometimes be touched up from behind with mirror touch-up paint, but this is a complex repair. For significant mirror scratches, replacement is usually more practical.

Is cerium oxide safe to use indoors?
Cerium oxide is generally considered safe but should be used with adequate ventilation. Avoid inhaling the dry powder. The wet slurry used during polishing is much safer than dry powder. Wear gloves and eye protection when mixing and applying.

Final Thoughts

Glass scratch repair with cerium oxide is one of the more satisfying DIY repairs — a scratch that seemed permanent can be polished away with patience and the right technique. The key rules are: assess the scratch depth honestly before starting (very deep scratches may not be fully repairable), keep the surface wet during polishing, work in overlapping circular motions over an area larger than the scratch, and check progress frequently. For surface and moderate scratches, the results are nearly invisible. For deep scratches, polishing significantly reduces visibility even if it can't eliminate the scratch entirely.