Because all organic materials contain moisture, fluctuations in temperature and the resulting changes in relative humidity will cause objects to expand and contract. Over time, continuing dimensional changes will result in permanent damage to both organic and inorganic substances. This phenomenon is compounded in textiles made of disparate materials. Other problems associated with high relative humidity are bleeding dyes and corroding metals. Pollution and Airborne Soils Smog, car exhaust, and ozone are pollutants that cause chemical degradation of objects.
Textiles are also subject to physical abrasion and damage by dust and gritty particles.
These particles in combination with air pollutants may accelerate the rate of chemical reactions. Household cleaners, particularly those containing chlorine, bleach, and ammonia, are also sources of chemical pollution. The materials used in exhibition cases, frames, or storage units must be carefully selected to ensure environmental stability. Wood, cardboard, and many plastics and metals are considered unsatisfactory because they emit volatile acids or chemicals. If these materials are the only ones available, place a barrier of stable material, such as heavy-duty aluminum foil, between the object and the support.