Solid brass does tarnish. Some people like the look of tarnished brass better than polished brass. While your dog is wearing a solid brass tag, depending how active he is, he is constantly rubbing it on his coat and other obstacles. This alone will usually keep the dog tag in a polished brass state. However, if your dog is not wearing his tag for extended periods, it may tend to tarnish from the elements - humidity, etc. depending on wear and how it is stored. To learn more about how to make your brass tag look like new, check out our brass care blog post.