Degradation in optical media refers to the decline of the physical quality of CDs, DVDs and Blu-rays over time and can be ascribed to material and environmental factors.
Material factors include:
- The disc format. A CD-ROM has a different composition than a CD-RW and therefore deteriorates at a unique rate. Refer to proceeding paragraphs to see how each type of disc is affected by its raw parts.
- The manufacturer. Each company employs their own version of dyes, plastics and alloys, which in turn cause discrepancies in quality between brands. This also includes the assembly of the discs themselves.
- The quality of equipment used in conjunction with the disc. Incompatible writing speeds or low-end equipment will weaken the disc faster.
Environmental factors include:
- Exposure to high temperatures. Heat buildup speeds the degradation process by breaking down the recording layers of discs that employ organic dye compounds.
- Excessive humidity. High moisture content that can seep into disc cracks or scratches and foster the growth of bacteria or mold that can affect the readability of the disc by a drive's laser.
- Consistent contact with UV (ultraviolet) rays. Sunlight accelerates the aging of the disc by altering the appearance of the recording layers and therefore rendering the disc ineffective.
- Dust, dirt and other air pollutants. These foreign particles can accumulate on the media's surface and in between its crack or scratches. They can not only damage the disc, but they can also cloud reading and recording functions.
Improper handling or storage will also contribute to a faster deterioration process of CDs, DVDs and Blu-rays. Conversely, no matter how well discs are treated by the user, degradation can only be controlled to a certain extent, as they have a limited shelf life. The core recording layers of a disc will naturally break down before the outer plastic substrate layers. The outer polycarbonate substrate incurs damage mainly from rough handling, and is therefore not considered when measuring the disc's overall shelf life.
The first signs of disc degradation are typically imperceptible because any abnormalities are detected and corrected by the media's inherent error system. Through further decay, a user will be able to pick up jitters and other errors which mean the error coding system is losing its ability to function. The more errors that subsequently arise, the closer the disc is to being ineffective for use.
The variation in compositional elements between the formats of CDs, DVDs and Blu-rays contributes to what is specifically responsible for the disc's degeneration. For example ROM, R and RW/RE formats will have varying levels of decay. CD-ROM/DVD-ROM/BD-ROMs contain a metal alloyed data layer derived from aluminum. Consequently, degradation occurs when this metal oxidizes and reduces the layer's shine. Without the shine, there's less reflectivity which translates to a laser's inability to properly read reflected data.
CD-R/DVD-R/BD-R employs recording layers made with dye that can be prone to accelerated decay. Since the dye is chemically altered when a drive's laser reads or writes its data, it is extremely photosensitive. Even mild exposure to UV rays can affect the longevity of the discs. The disc's reflective side will visibly convey dye degradation over time through dark color discrepancies that don't match the green, gold, blue or silver appearance of a new disc.
The composition of CD-RW/DVD-RW/BD-RE has two primary factors working against a prolonged shelf life: metallic alloyed layers and a phase changing alloyed layer. The phase changing alloy lacks the stability of discs that employ dye, making them prone to major damage from UV light. The oxidation of the metallic reflective layers additionally counts against its potential for longevity. RW discs are also not purposed for long term or archival use. Their erasable and re-recordable nature is limited to less than 1,000 rewrites, meaning after they reach this capacity, their ability to function is degraded.
For more information on the proper care and handling of CD and DVD optical discs, please visit the guide entitled Care and Handling of CDs and DVDs published by the National Institute of Standards and Technology.
- CD/DVD Degradation
- Gold Discs Explained
- Lifetime of Kodak CD Media
- Lifetime of TDK CD Media
- Media Longevity
- Recordable Media Quality and Longevity
- Special Report: Media Longevity