What can I use to restore granite countertop?

A few years back I made an outdoor table and used a large peice of leftover granite that was used for a granite countertop as the top. In the years it's been outside the sun has destroyed whatever they used to give it its sheen and it has become very rough. I was wondewring if there is anything out there to at least remove the sunbleaching effect because when I use something wet to clean it the origingal color comes out.