Glass is a funny thing. It’s a two-way mirror and a transparent wall. At the same time, one can look through it and at your own reflection on it. Glass is weird because it is something so unfamiliar. It actually does occur naturally. Scientists call it a state of matter rather than a material – it occurs when some really hot matter has been rapidly cooled and has not had enough time to crystallise. Quite an exciting thought I think. Lightning strikes and lava pools can form glassy structures. In my mind right now is a picture of two cavemen using a mildly opaque obsidian as a skylight for their sea-side cave.