Jelly
This is another one of those "strange materials" type of examples but this time it is transparent opening up some possibilities with light. I Norway it is possible to buy Jelly (Jell-o to Americans) ready made in cartons. I'm not sure if this is available everywhere but the stuff i was used to In Britain was "Chivers Jelly" that came in small rubbery packets and you had to mix it with water. The ready made variety is...