'All that glisters is not gold': what is the origin of this well-known phrase?

'All that glisters is not gold' is a fairly well known phrase, often used today to suggest that something isn't quite what it appears to be. It was in use to a degree in Shakespeare's time and even earlier. In his talk John will explore how it might have come into use. This will involve some materials science (not too much!), some geography and some relatively unexplored history. John Forty will speak on this topic in Cottrell 2B76