They can cause yellowing of finishes, accelerated breakdown of paper and textiles, tarnishing and corrosion of metals, and etching of stone. Particulate pollutants, which include dust, cigarette smoke, and industrial fly ash, can cause damage in several ways. They contain abrasive particles that scratch surfaces and they contain mold spores or other organic material that provide a base for mold growth. In addition, they frequently have an oily component that allows particulates to become tightly bound to the surface, and they are hygroscopic, attracting moisture to the surface of the object, where soluble pollutants can dissolve and become chemically destructive. To avoid pollutant damage, objects should be kept as clean as possible, air conditioning filters should be changed regularly, and windows should be kept closed.
All wavelengths of light have sufficient energy to damage surfaces of objects.
Light actually can break down the structure of cellulose, the primary component of wood, paper, and cotton. Light damage is cumulative and cannot be reversed . Even wooden objects from tombs of Egyptian pharaohs still have the capability to expand and contract in response to changes in humidity. The perceived dryness on a piece of furniture is usually a condition of the finish, wherein it has become crackled from age, where shrinkage of the film of finish may have resulted in its cleaving from the wood, and the aged finish is generally covered by a layer of embedded dust. Unfortunately, the process doesn't stop when the film is hard but still clear.