ABSTRACT
Stable RH is critical for museum objects. Changes in RH create dimensional changes in organic museum objects, e.g. wood, leather, textiles, ivory, bone, paper, etc. These changes can cause expansion and contraction of materials and irreparable damage can result. Organic materials are also liable to attack from moulds/fungi if conditions are humid, over 65 per cent RH (see Units 58, 60-1). Metallic objects can also be adversely affected by high levels of RH, which encourage corrosion. RH needs to be as low as possible for all metallic objects.
