Over time, the silver backing that gives a mirror its reflective nature can crack, erode or chip. This doesn't mean you have to get rid of the mirror. There are a variety of methods you can try to strip the silver backing from your old glass mirror and give it new life. Most use chemicals that are highly corrosive, so it is necessary to use caution while applying the products.
Put on rubber gloves. Mix a small amount of lye with warm water. The stronger the brand of lye you use, the less you'll need.
Turn the mirror over, so the nonreflective side is facing up. Place the mirror on a flat surface, preferably outdoors.
Pour the lye mixture over the back of the mirror.
Allow the lye mixture to sit on the mirror until you notice the silver paint becoming soft.
Mop up the silver paint using a wet rag.
Repeat steps 1 through 5 until all the paint is removed.
Buy undiluted nitric acid from a chemical company. Nitric acid is a compound found in fertilisers, so it may be hard to find in small amounts.
Place the mirror on a flat surface, preferably outdoors. Have the mirror's back side facing upward.
Put on rubber gloves. Pour a small amount of the nitric acid onto the back of the mirror.
Wait for the silver paint to turn soft; it may bubble.
Remove the silver paint using a warm, wet rag. Repeat the above steps until the paint is completely removed.
Purchase a mirror-stripping kit from your local hardware store. These kits contain two different combinations of chemicals that will soften, then strip the silver backing from the mirror.
Put on rubber gloves. Pour the first chemical onto the back of the mirror, using the quantity specified on the kit's instructions. This amount will vary depending on the size of the mirror.
Apply the second chemical onto the mirror.
Use a warm, wet rag to remove both chemicals. Repeat the above steps until the process is complete.
Buy a pack of razors for this project. This is the slowest and most painstaking of the four options to strip a mirror, and will require multiple blades, depending on the size of the mirror.
Sharpen the razor blade, removing any dull edges.
Scratch off the silver paint on the back of the mirror. Be careful not to scratch the glass itself, as this will ruin the mirror.
These options for stripping a mirror range from easy to difficult; the options that use chemicals require significantly less manual labour than the razor blade option. Remove any frame surrounding the mirror before stripping the silver backing off the glass. If a wet rag isn't enough to remove the dissolved silver paint, try a stiff piece of cardboard. Pull the cardboard against the mirror's surface, applying pressure to scrape the paint off. Clean the glass using a mild detergent or warm water before repeating the cycles. This will maximise your results and minimise your time. Some mirror-stripping kits work best when the mirror is warm: at least 21.1 degrees Celsius. Read the directions on any kits you purchase from a store before use.
All the chemicals used are highly corrosive, and can do serious damage to the eyes and skin. They can also be harmful if breathed in large quantities. Use proper protection, including gloves, to protect the skin. Work in an outdoor space to minimise dangerous fumes.