Bill,
I would say use what works for you but keep an eye out for another mirror. If you come across one that you just like for some unexplained reason, that would be a good one to try and work with, It could just be that the black mirror you're working with isn't conducive to scrying. Although mirrors aren't alive, they have individual qualities to them and when you find a good one it's a great tool to have.
Lorrie