Replacements are purchased where possible. Otherwise, materials are microfilmed or photocopied on alkaline paper that will last for several hundred years. This is an example of brittle paper. Once paper reaches this stage of embrittlement, and is unusable, it must be reformatted. These two pictures below dramatically illustrate how information can be archived on preservation master negative microfilm., which, if properly stored, will last for hundreds of years.
Users can, at any time, request a copy of the materials stored on the film.