User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-5043481-20120903174919/@comment-5043481-20120910155656

There's a problem with refraction. If you want something to turn invisible you need to have the light rays going in the same direction as when they hit the object on the other side. To do this you could make the object transparent, but then the refraction is a problem as the light exits in a different direction. And presumably you want to have somethng in the middle, so it is difficult.