gases that cause chemical deterioration, as well as dust and particulates that can cause abrasion. Sources of indoor pollution that affect photographs include paint fumes, plywood, cardboard, and cleaning supplies. Exposure to light causes embrittlement, fading, and yellowing. The damage is cumulative and usually irreversible. UV light (including from sunlight and fluorescent light) and visible light in the blue part of the spectrum are especially harmful to photographs, but all forms of light, including incandescent and tungsten, are damaging. Mold growth is fostered by high temperatures and humidity as well as dust particles. They cause damage to the surface of photographs and help break down binder layers. The presence of insects and rodents is also fostered by high temperatures and humidity. They eat paper fiber, albumen, and gelatin binders, leaving chew marks and droppings. Species likely to cause problems include cockroaches and silverfish. Other factors Inappropriate storage containers and repair attempts: Cabinets made of inferior materials can give off harmful gases, while other reactive materials such as acidic paper sleeves, rubber bands, paper clips, pressure sensitive tape, and glues and adhesives commonly used for storage and repairs in the past can also cause chemical deterioration. Storing items too loosely, too tightly, or in enclosures that do not provide adequate physical protection can all cause physical damage such as curling and breakage. Human handling and use, including by researchers and staff, can also cause both chemical and physical deterioration. Oils, dirt, lotions, and perspiration transmitted through fingerprints can destroy emulsion and cause bleaching, staining, and silver mirroring. Physical damage caused by human handling includes abrasion, scratches, tears, breakage, and cracks. Improper chemical processing, including use of exhausted fixer, insufficient length of fixing, and residual fixer left behind by inadequate washing can cause fading and discoloration. Heat, humidity, and light can accelerate such damage. Adherence to ISO standards at the time of processing can help avoid this type of deterioration. Examples of threats to specific photographic materials Glass plate negatives and ambrotypes are prone to breakage. Deterioration of film negatives, regardless of type, is humidity and temperature dependent. Nitrate film will first fade, then become brittle and sticky. It will then soften, adhere to paper enclosures, and produce an odor. Finally, it will disintegrate into a brown, acrid powder. Because of its flammability, it must be handled with particular care. Cellulose aetate, diacetate, and triacetate film produce acetic acid, which smells like