Methods for preventing deliquescence, efflorescence and hydration in use today include: (1) coating with lacquers, (2) refrigeration, (3) storage in sealed containers at the mineral solution equilibrium relative humidity, (4) storage at the mineral equilibrium lower or mineral equilibrium higher hydrate equilibrium relative humidity, or (5) storage at an enforced intermediate relative humidity. The utility of lacquers is limited by their low efficiency as vapor barriers. Refrigeration alone will at best slow reaction rates. Storage in sealed containers at mineral equilibrium solution equilibrium conditions risks morphological changes since the solution phase permits ion mobility. Storage in a sealed container at higher equilibrium lower hydrate equilibrium conditions requires perfect hermetic sealing; this can be difficult to achieve in practice. Storage in a sealed container at an enforced relative humidity requires that the stability limits of a specimen be known with sufficient accuracy. Although problems are associated with all these methods, the last two (4) and (5) are limited only by technical difficulties and are therefore considered the most suitable for long term preservation of specimens. See also AATA 17-968.