iblink asks: "Last year Fujifilm stopped producing a color slide E-6 sheet film called Velvia 50. It has unique color characteristics that I love so I decided to purchase the remaining stocks in Europe. I now have hundreds of boxes that need to be stored for up to thirty years. A number of film experts assured me that freezing the Velvia would stabilize the dyes for long term use. However, they all mentioned that cosmic radiation would eventually fog the film, and they offered little help in finding a relatively inexpensive barrier. I found various ideas on proton cosmic radiation barriers — a big bucket of water, lead, certain plastics — but nothing convincing or sufficiently detailed (which plastic? How thick?). The film is currently in a freezer, unprotected. Any ideas?"