Archives facilities, clear plastic bags such as Zip-locks or flush-cut bags with twist-ties (polyethylene or polypropylene plastic bags) and cotton gloves are needed. Removing items from cold storage requires letting them acclimate to room conditions. Photographs must be allowed to warm up slowly in a cool, dry place, such as an office or processing area. Original items should be retrieved from the storage only in an emergency and no more than once a year. Without cold storage, temperature-sensitive materials will deteriorate in a matter of a few decades; with cold storage they can remain unchanged for many centuries. Light control Photographs should not be hung near light. Hanging photographs on a wall can cause damage from the exposure to direct sunlight, or to fluorescent lights. Displays of photographs should be changed periodically because most photographs will deteriorate in light over time. UV-absorbing sleeves can be used to filter out damaging rays from fluorescent tubes and UV- absorbing sheets can be placed over windows or in frames. Low UV-emitting bulbs are available. Light levels should be kept at 50–100 Lux (5–10 footcandles) for most photographs when in use for research as well as exhibit. Exposure of color slides to the light in the projector should be kept to a minimum, and photographs should be stored in dark storage. The best way to preserve a photograph is to display a facsimile. Pollution control Controlling air quality is difficult. Ideally, air entering a storage or exhibition area should be filtered and purified. Gaseous pollution should be removed with chemical filters or wet scrubbers. Exterior windows should be kept when possible. Interior sources of harmful gases should be minimized. Metal cabinets are preferable to wooden cabinets, which can produce harmful peroxides. Air can be filtered to keep out gaseous pollutants and particulates such as nitrogen dioxide, sulphur dioxide, hydrogen sulfide, and ozone. Air filters must be changed regularly to be effective. Air circulation should also be checked periodically. Handling control Handling and use policies should be established and staff should be trained in policies and policy enforcement and telling users the policies when they arrive. Policies for processing, handling for loaned or exhibited items, and disaster prevention and recovery should also be created and followed. Work spaces should be clean and uncluttered. Clean gloves or clean, dry hands should be used whenever photographs are handled. Foods, drink, dirt, cleaning chemicals, and photocopy machines should