An oxidising substance was formed which attacked the resin coating resulting in cracking. The oxidant also attacked the silver image and bleached it. External Deterioration Factors External deterioration factors are harmful substances in the preservation environment. Among the many contaminants, a few should be particularly mentioned. Furbishing in repositories should not consist of materials emitting oxidising gases.
Oxidising gases react with photographic materials in a similar way as common air pollutants.
High temperature and relative humidity accelerates these processes. Good storage conditions will counteract deterioration of materials with bad ageing properties to a certain point, while bad storage conditions will always accelerate deterioration processes. The best way to preserve photographic materials is to emphasise measures on preventive care. The passive archive should have a stable climate with low temperature and relative humidity. A number of recommendations exist but they do not differ significantly from the requirements listed in the following table.