Optical Media Preservation - Damage To Optical Discs - Environmental Considerations

Environmental Considerations

Optical discs can be damaged by exposure to extreme temperatures; direct sunlight may overheat the disc or damage the data layer with UV rays. Exposure to heat and light have different effects on discs with data and metal layers of different composition. In all optical discs high temperatures can cause the substrate to soften and the disc to warp. Ambient heat, heat build-up, and light do little to damage the data layer of a ROM disc as it is made of aluminium; the only known problem occurring with the prolonged exposure of ROM discs to light is "clouding" or "coloring" of the polycarbonate substrate. CD-R, DVD-R, DVD+R, CD-RW, DVD-RW, DVD+RW and DVD-RAM discs are all affected by exposure to ambient heat as well as heat build-up due to direct sunlight. A CD-R’s data layer is made of dye that degrades at high temperatures, becoming less transparent so that bits and lands are read incorrectly, making the data unreadable. UV rays in sunlight are energetic enough to produce a photochemical reaction that changes the optical properties of the dye. RW and RAM discs' data layers are composed of a phase-changing film that is even more sensitive to heat than the dye found in R discs, so that they degrade even faster when subjected to ambient heat or direct sunlight. The phase-changing film in RW and RAM discs is not light-sensitive, and UV rays do not affect the optical properties of the film. After being exposed to freezing temperatures a disc’s separate layers may warm at different speeds, causing separation of the layers. If heated or cooled significantly a disc should be allowed to return to room temperature before use.

The polycarbonate substrate of discs exposed to high humidity or immersion may absorb some water, and should be allowed to dry out in a less humid environment before being used. After drying discs should be usable unless minerals left behind from the water react with the components of the disc, damaging the layers and making it unreadable, as sometimes happens.