That was actually the premise of a set of short stories by Bob Shaw -- the slow glass stories. The premise was that someone discovered a material with an absurdly high index of refraction, and that it was used as a video recorder: you left the slow glass outside in the summer, and hung it on the wall in the winter, so you had a summer view year-round. They were charming stories, if, like Bob Shaw, you ignored the fact that leaving the stuff out for a summer would give it energy densities several orders of magnitude higher than dynamite. :)