Removing the silver from mirrors is effective when trying to repair or refurbish an old mirror or when trying to make your own personal one-way mirror. This process takes time and a number of reasonably potent chemicals, so make sure you wear rubber gloves and old clothes that you don't mind ruining or bleaching if chemicals happen to spill or splash on them. Some more painstaking solutions take a lot more time.
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As the silver on mirrors is just paint that has been created out of silver nitrate solution and painted onto a piece of glass, running a razor blade across it to scratch off the solution usually does the trick just fine. However, this is a long and painstaking process and is as slow as taking old paint off an old picket fence. Make sure you buy a pack of razors and a tool that will hold the razors to make it easier on your arm while you do the scraping. Be careful not to scrape the glass itself, or you will ruin the mirror.
Two-Part Stripping Kits
Most stain glass shops carry two-part mirror stripping kits. The kits consist of two types of chemicals that liquidize the paint surface but leave the copper mirror service intact. A second chemical layer which is a stripper dissolves the next two mineral layers, leaving you with perfectly clear glass. This method can be used with strips of tape or sandblasting, so you can create patterns, like line strips of mirror on glass itself or frosted glass, adding an artistic flare to certain mirror projects.
Lye and Water
By simply mixing strong lye and water, you can pour this mixture onto the mirror itself. Be careful because lye will burn you, especially when mixed with water. So wear gloves, and take the necessary precautions. Let the mixture stand for a bit until the silver paint is soft. Then mop it all up, and dispose of it in a separate container to take to a chemical treatment facility. Sometimes all the silver paint won't come up in this fashion, so a razorblade or hard piece of cardboard will be necessary to scrape it the rest of the way.