Oxidized silver happens when silver is exposed to the air for too long. Getting technical, a compound called silver sulfide forms, and darkens the finish. Some types of jewelry are made this way on purpose, and they have a darker look. If your silver is severely oxidized, please talk to someone that specializes in silver restoration. Unfortunately, if you use chemicals that are too abrasive, you could damage your silver. That being said, my method will work on cleaning tarnished silver that isn't badly oxidized. Keep in mind that old silver that's been around a while will not only have tarnish, but other spots and marks. Sometimes these can be removed, and sometimes they can't. The secret is to embrace the imperfections, and appreciate the beauty of your vintage item.