However, even placement within a few inches can gradually degrade an unshielded disk or tape. Even in a pristine environment, magnetic media have a shelf life. Tapes are liable to magnetic print-through. All media, but especially tapes, are liable to the unavoidable chemical breakdown of long molecules and larger particles. The formulations that allow higher storage densities involve complex substrates, binders, particles, and lubricants.
Complexity feeds entropy.
Ample research and experience provide evidence of what can go wrong with magnetic media as a result of binder degradation, magnetic particle instabilities, and substrate deformation. Optical media are susceptible to damage from high humidity, rapid and extreme temperature fluctuations, and contamination from airborne particulate matter. To prevent these problems, it is very important to store magnetic and optical media under strict environmental controls that are not always available, affordable, or convenient. Even modest improvements which produce storage media with larger per unit storage capacities and greater tolerance to variations in temperature and humidity will lower preservation costs. The only magnetic reasons for an unsuccessful data recovery are erasure or extreme temperature exposure.