It's an interesting subject, and i've some experience of photographic preservation having printed in darkrooms for 20 years or so. When considering archiving o

It's an interesting subject, and i've some experience of photographic preservation having printed in darkrooms for 20 years or so. When considering archiving old photographs, there's quite a bit of difference between colour and B&W prints, and also colour and B&W negatives. The B&W prints and negatives contain silver, which is what makes the dark spots on the print and negatives, and it's presence stops microbes attacking the material. For colour prints and negatives, the silver that was originally present in the material is removed with a bleach stage when processing (with a dye being activated to produce the colours you see) so you need to use some other method to protect the material from microbes. I think modern colour film stock includes a stabilizer, whilst older processing used Formaldehyde.