Prep first
Before you start
- Work out the cause first: where the mark sits, how it smells and feels, and how it appeared.
- Test any cleaner on a hidden spot first.
- Brush dry soot or mildew off before you wet it.
Black spots on glass, such as a bathroom mirror, usually come from mildew, soot or greasy residue, and some are damage rather than dirt. Those damaged spots stay even after a careful wipe, so it helps to know which kind you have. A fresh spot often lifts with a gentle clean, while an old one on an aged mirror may only fade a little.
Work from the center of the spot outward on the mirror, keeping the cloth barely damp so moisture doesn't seep under the edges. Once improvement stalls on black spots on an old mirror, stop scrubbing rather than pushing harder. If a clean cloth shows nothing new after a few tries, call a glass professional.
Before you start
What glass, windows & mirrors can take
Safe to use1
- Water
Use with care7
- Hot water
- Soaking
- Chlorine bleach
- Solvents (alcohol, spot removers)
- Acids (vinegar, lemon)
- Scrubbing and abrasives
- Heat, once the stain is out
5 items
What you'll need
Tap an item to get it on Amazon, or tick what you already have.
- Soft microfiber clothsOne for the soap wipe, one for the alcohol wipe and one dry for buffing. (opens Amazon)
- Mild soapFor the first wipe in warm water. (opens Amazon)
- Isopropyl alcohol, 70%Mixed with water for the final wipe. (opens Amazon)
- Soft brush or a vacuum with a brush attachmentFor dry soot and mildew before anything gets wet. (opens Amazon)
- Alcohol wipes (opens Amazon)
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6 steps
Step by step
Step 1 of 6
Find the cause and test first
Look at where the black mark sits, what it smells like, how it feels and how it appeared, since those decide the treatment. Then test your cleaner on a hidden spot, such as a corner of the glass that the frame covers.
Careful. Some black marks are damage rather than dirt, and cleaning won't lift them.
Step 2 of 6
Brush off dry soot and mildew
Brush or vacuum dry soot and mildew before you wet them, so you don't smear them across the glass. If the growth is mildew, brush it off outdoors where it can't drift back into the room.
Step 3 of 6
Wipe with mild soap and warm water
Dampen a soft cloth in warm water with a little mild soap, then wipe the black spots and a band around them. Use light, overlapping strokes and keep going until the cloth comes away clean.
Tip. Wring the cloth well so it's damp, not dripping.
Step 4 of 6
Wipe with the isopropyl alcohol mix
Mix 50/50 water and isopropyl alcohol, then spray the cloth, not the mirror. Wipe the spots and the glass around them, turning to a clean side of the cloth as it fills with grime.
Careful. Spraying cleaner directly onto a mirror can damage its edges and backing.
Step 5 of 6
Rinse with clean water
Wipe the mirror with a clean cloth dampened with plain water to lift any soap and alcohol film. Rinse thoroughly after any cleaner, since leftover film can dry as haze.
Step 6 of 6
Dry and check the spot
Buff the glass dry with a clean soft cloth, working from the top down so drips don't run into the dry area. Check the spot in good light from a few angles, and if it's still there, repeat the soap and alcohol wipes once more.
If you'd rather buy than mix
Best products for black stains on glass, windows & mirrors
Pick 70% isopropyl alcohol with no added color or fragrance, and test it on a hidden spot before using it on the mirror.
Amazon Basics Microfiber Cleaning Cloths
e-cloth General Purpose Cloth
How we picked these: each product is made for this type of stain, its maker doesn't warn against using it on glass, windows & mirrors, and its directions fit the steps above.
Finished the steps? How does it look?
Nice work. Let it dry completely and check it again in good light. Here is what done looks like:
How to tell it's really gone →A faint mark usually needs one more round, not a stronger product.
Heavy buildup usually takes more than one round.
Heavy or long-standing buildup →When to call a professional →How to tell it's working
When the spot lifts, the cloth comes away with a gray or black smear and the glass looks even. If the mark survives one full round of wipes, the set-in notes below explain what's realistic.
What changes for yours
Adjust for your glass, windows & mirrors
Mildew on a bathroom mirror
Brush the dry growth off outdoors if you can, so the spores don't drift back into the bathroom. Don't cover or paint over mildew, since it keeps growing underneath.
After brushing, use the soap wipe and the alcohol wipe, then check the corners and edges where moisture sits longest.
Soot from a candle or fireplace
Soot should be brushed or vacuumed dry before any liquid touches it. Wetting it first tends to smear it across the glass.
After the dry pass, use the soap wipe and the alcohol wipe, then rinse. If soot is still there after that, the set-in notes below cover what's realistic.
Mirror edges and corners
Wring the cloth out until it's just damp, then wipe along the edges and corners in short strokes. The edges and backing are the parts most at risk, so keep the cloth from pooling liquid there.
Finish the edges with a dry cloth so no moisture sits along them.
Glass tile
Glass tile needs a non-abrasive cleaner recommended for glass or tile. Let heavy soil dwell 3 to 5 minutes per the product label, then rinse with clean water.
Never use scouring pads, steel wool or sandpaper on glass tile. The Grout guide covers the lines between the tiles.
Glass dishes and ceramicware
Use a non-abrasive cleanser on glass and ceramicware, and a plastic or nylon pad only if scouring is needed. Rinse thoroughly after any cleaner so no film is left behind.
Avoid sudden temperature changes: don't add liquid to a hot dish or set one on a countertop, metal surface or in the sink, since it can break. The Dishes & Mugs guide covers everyday washing.
Heavy or long-standing buildup
Old black spots have often been there long enough that a single wipe won't shift them. Repeat the soap wipe and the alcohol wipe once more, using a clean side of the cloth each time.
If the spots have dried on and feel gritty, brush off what you can dry before wetting them again. Rinse with clean water between rounds so no film builds up.
If the spots stay after two rounds, they can't be lifted by cleaning alone. Some marks just can't be fully removed, so aim for a lighter result, since stronger products aren't a safe next step on a mirror.
Vinegar, baking soda, peroxide and more
Do home remedies work on black stains on glass, windows & mirrors?
Many household remedies are built for fabric, counters or wine, so most don't belong near a mirror. Mild soap, warm water and a cloth dampened with an isopropyl alcohol mix suit a mirror.
Works1Skip4Avoid1
What makes it worse
Mistakes to avoid
Don't use vinegar or ammonia on a mirror.
Both are ruled out for mirrors, so keep them out of the bucket and off the cloth you use on the glass. The mild soap and the isopropyl alcohol mix in the steps are the cleaners to reach for.
Don't use chlorine bleach before you know the cause.
Bleach can intensify manganese and iron stains, which can look black on glass. Work out what the mark is first, and if you can't tell, leave bleach out.
Don't use fluorine cleaners on glass.
Cleaners with fluorine compounds damage glass, ceramic and stone. Read the label before buying any cleaner for the mirror or other glass in the room.
Don't scrape the glass with metal or hard objects.
Razor blades, scrapers and similar tools are not safe on glass, however stubborn the spot looks. The soft cloth and the soap and alcohol wipes do the work instead.
When to call a professional
If the black spots sit behind the glass and cleaning changes nothing, a glass specialist can tell you whether the mirror can be repaired or needs replacing. Ask them to check the edges and backing before they quote a fix.
Questions
Why are there black spots on my mirror?
Most black spots are dust, soot, mildew or grime that has built up on the glass. Testing a hidden spot and watching how the mark responds to a soap wipe will show you which one you have.
Can I clean black spots on a mirror with vinegar?
No, not on a mirror. Vinegar is ruled out here, so use the mild soap wipe and then the alcohol wipe from the steps instead. Those two cleaners handle these spots without the risk.
Will black spots on an old mirror come off?
Some will lighten after a couple of rounds of wipes, but some can't be fully removed. Repeat the soap and alcohol wipes once more, and stop if the spots don't change.
Can I cover mildew on a bathroom mirror and leave it?
No. Covering mildew doesn't stop it, since it keeps growing underneath. Brush off the dry growth first, outdoors if you can, then clean the glass.
Can I use steel wool on glass tile?
No. Scouring pads, steel wool and sandpaper aren't safe on glass tile. Use a non-abrasive cleaner recommended for glass or tile, then rinse with clean water.
Do I need to test a cleaner first?
Yes, test any cleaner on a hidden spot before using it on the black mark. A small test shows you whether the cleaner is safe on the glass and whether the mark responds.
Black Stains on other materials
Other stains on glass, windows & mirrors
Start from the bigger picture
How we know this
Every method, amount and warning here comes from university extension services, industry bodies and product makers. We read them, check every step for unsafe combinations and changed amounts, and write it up so you can follow it.