You can do that with Butter!

I have a friend who works in particle physics, x rays and all kinds of stuff. I was chatting to him about an idea I had to teach young people about the consequences of misusing digital information. This became about because I was asked by a client if I could come up with an idea to dissuade young people from giving songs and videos to each other free that someone somewhere had originally pirated. I started researching ways of mechanically recording sound and did some experiments with needles and paper. Haven't cracked it yet but i think i will when I get the recording strip right!
So i am in the pub talking to my scientist friend about this and he says 'you can record sound with a needle on butter'. Its three weeks later and he still has not been able to show me where this has been done!
My recording prototype doesn't use butter, it uses aluminium but I am trying different materials till I get something that is not only workable, but also easily reproducible. I am sure that one off, for one time only, using very careful temperature control techniques someone did manage to record sound onto butter... it seems to me quite feasible, but education needs solutions that work in the real world at room temperature and can be reproduced by others without huge technical skills and budgets!
A good project needs proof and a manual, A rumour is untested!