So how about a steel plate (mounted on a lightweight aluminum frame for instance), painted by a professional painter to a piano black finish? It's quite sturdy to start with, and minor scratches can be polished out. Again, the option will be a tad on the expensive side, and if loaded with too much pressure/supported wrong it will bend, which will look ugly in the reflections, but it's far more durable then the plexiglass option. And lighter then granite or glass.