Incorrect relative humidity can be broken down into four subgroups:
damp (over 75%), above or below a critical value, above 0%, and
fluctuations. Mould growth can occur when the relative humidity
is over about 75%, and certain minerals or contaminated metals
deteriorate above or below critical relative humidity values.
Some chemical deterioration reactions slow as the relative humidity
is reduced, and stop when the relative humidity drops to 0%. Relative
humidity fluctuations cause swelling or shrinkage of organic components,
which can result in fracture, crushing, or delamination of organic
components. Although incorrect relative humidity can result in
considerable damage to vulnerable artifacts, in most cases it
does not lead to complete destruction of artifacts.
Costain, Charlie. Framework
for Preservation of Museum Collections, Canadian