Relative humidity and temperature levels determine whether these organisms flourish or exist at all. Mechanical deterioration is related to either the amount of water absorbed by organic materials, or thermal expansion in inorganic materials, especially metals. The item changes size and shape, leading to cracking, splitting and warping. Stress or the application of different materials will affect the susceptibility of a piece to mechanical deterioration when the environment fluctuates. Chemical Deterioration Chemical reaction rates increase with higher temperature, increased concentration of reactants and increased pressure.
Water is a reactant in many decay processes.
Increased relative humidity increases the concentration of water. The Image Permanence Institute has researched the chemical decay of archival materials, especially film and photographs. Not everything lasts the same amount of time. Each material has a unique decay rate. For example, among papers, rag paper is slow and newspaper is fast, but both decay rates increase with higher temperature and relative humidity.