How do you get rid of the black areas (maybe mold?) under mirrors?

You may have to purchase mold removal liquid from Walmart or such, bleach doesn't always do it. Bleach mixed with water leaves the water to feed the mold mildew once again.

If it's on the glass itself the coating on the back to make it reflective is probably deteriorating as in antique glass. It is just a guess that moisture somehow got in between the layers I am including a link that might help www.google.com/search?q=how+to+repair+mirror+silver&oq=how+to+repair+mirro&aqs=chrome.4.0j69i57j0l4.12631j0j7&sourceid=chrome&ie=UTF-8 Good luck

That is probably damage to the silver coating on the lower backside of the mirror...from water or moisture seeping under your mirror where it meets the backsplash behind the sink. You will probably have to take the mirror down and get the damaged area re-silvered. Or, there is a mirror type of spray paint available now...maybe you could spray the damaged area on the back of the mirror with that paint, rather than a professional re-silvering.

Donna is correct. Moisture has gotten under the paint coating on the back and attacked the silvering. Really no way to repair. Most people frame the mirror to hide the damage.

Start with full strength vinegar, Don't get any on the mirror.

50/50 bleach / water

Mirror may just be showng signs of age and going "blind" from the moisture. You can have re silvered (I have had this done), or they sell DIY kits at hardware and home improvement stores. I have never used the kits, so can't comment on how well they turn out.

It is most likely mold. Moisture condenses on flat surfaces like mirrors and runs to the bottom where it is slow to dry making mold the likely culprit. Laundry bleach, (Clorox) or hydrogen peroxide should do the trick. (Either product had the ability to discolor certain materials and finishes by their bleaching action, proceed with caution).

William is right. This will give you some ideas.

https://www.google.com/search?q=reframing+old+mirrors&rlz=1C1BLWB_enUS700US700&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi9z5TVhNXXAhVJ9mMKHSpSBFgQ_AUICygC&biw=1422&bih=684&dpr=1.13

To remove black areas (which may be mold) under mirrors, you can try the following steps:

1. First, remove the mirror from the wall. Be careful to handle it gently and keep it away from any moisture or water sources.
2. Clean the back of the mirror with a dry cloth to remove any dust or debris.
3. Inspect the back of the mirror for any visible signs of mold. If you do see mold, it is important to act quickly to remove it before it spreads.
4. Mix a solution of equal parts water and white vinegar.
5. Using a clean cloth or sponge, apply the vinegar solution to the back of the mirror, scrubbing gently to remove the mold.
6. Rinse the mirror with clean water and dry it thoroughly.
7. If the mold persists, you may need to use a stronger cleaner, such as a commercial mold and mildew remover. Follow the instructions on the product label carefully and test it on a small, inconspicuous area before using it on the mold.
8. Once the mold has been removed, replace the mirror on the wall. To help prevent the mold from returning, make sure the wall and the back of the mirror are dry before replacing the mirror. You may also want to consider using a dehumidifier in the room to reduce the humidity levels and help prevent the growth of mold.

Vinegar will kill the mold. Is the mold on the wall or the mirror itself?