Not a coin collecter, but I shot a collection before selling it for a family member. I used a copy stand that had lights on either side that allowed a lower angle (45 degrees or closer to the table top). As Greg said, lower the angle of your light source. You shouldn\'t have to use a polarizer, but you always could if necessary.
I also took a large translucent Glad food container and cut a hole in the bottom of it and shot through it. The container acted as a diffuser, along with some white sheets of paper. I also used a gray cardboard to place the coin and slide it under the setup. The cardboard also was used for WB.
