To my current(somewhat pathetic) knowlege the reflection off metal surfaces happens because the changing electric and magnetic fields cause "mini currents" or charge redistributions which produce their own electromagnetic waves identical to the incoming ones or in other words the reflection. My guess is that resistance and the fact that metals really aren't a continuous sea of charge (but more like a few electrons moving fairly freely in a crystal lattice) make the reflective abilities of metals less than perfect. But how close do you get with a superconductor? Maybe it was just the condensation due to the cold temperatures or a little oxidant layer or protective coating but i can't remember superconductors being particularly bright or shiny. And if there is no fundimental misconception about that model of reflection then i would be interested to know where it breaks down. The thought that very high gamma ray photons should be reflected off a superconductor is absurd. So why doesn't it happen ?