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Tuesday, March 30, 2010

CD-R For Long-Term Digital Storage of Photos, Audio, and More

By T. Millson

Depending on your storage requirements, a CD-R or recordable CD can be an excellent choice for safeguarding your digital information. Digital files such as digital audio, digital photos that are not very high quality, emails, spreadsheets, and word processing files can all be stored quite well on the CD-R format. However, the capacity of the recordable CD is either 650 MB or 700 MB and because of this, there is not enough space to store significant amounts of digital video and at reasonably good quality. To store more than 15 minutes of digital video on a recordable CD would require heavy compression of the video and this would result in poor quality. Despite this limitation for digital video, the CD-R can be used for the effective storage of most other digital files.

There are various choices for CD-Rs that go beyond just selecting a particular brand. CD-Rs store information in a dye layer and there are three main types of dyes that are used. The three dyes are a phthalocyanine dye which is light green in color, a cyanine dye which is generally light blue in color, and an azo dye which is deep blue. The phthalocyanine dye is the most stable and does not degrade with elevated temperature or relative humidity and does not fade with light exposure. Both the cyanine and azo dyes are much less stable. These dyes are sensitive to degradation initiated by temperature and relative humidity and will fade with enough light exposure.

Another important part of the CD-R is the metal layer. The metal layer is found after the dye layer if looking at a cross-section of a disc from the bottom up. A disc is read through the base. The role of the metal is to reflect the laser light that reads the disc back to the player/reader detector after it reads the information in the dye layer. In order words, the metal layer is very important because it allows the laser light to produce a signal. Without the metal layer, the laser light would shine through the disc and no signal would be registered. There are three types of metal layers that are used in recordable CDs, silver, silver alloy, and gold. Gold is very stable and will not react. Silver will oxidize and corrode and so will silver alloy but to a lesser extent.

Therefore, if you want to store your information on very stable media, the recordable CD or CD-R with a gold metal layer and phthalocyanine dye is the best option. Choosing discs with other dyes and other metal layers can potentially give you much shorter lifetimes. Finally, it is also important to select discs that have a good scratch resistant top layer because this will help prevent irreversible physical damage to that all important metal layer.

For more information on using CD-Rs or other media for storage of digital information, please visit


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