How to choose recordable CDs and DVDs

Recordable CDs and DVDs can last 20 to 200 years or more. They may not be indestructible, but they are far more durable than records, tapes or magnetic media. Know your stuff and you might be surprised at how long they last you.

Commercially available audio CDs, CD-ROMs, and DVD movies have a life expectancy of only 20 years or more, while recordable CDs (CD-R) and DVDs (DVD-R, DVD+R) are expected to last 100 to 200 years or longer. But this doesn't apply to CD-RWs.

When archiving important data, such as digital photos and videos, original music or irreplaceable files, you want a recordable CD (CD-R) that will last as long as possible. The type of reflective metal layer and the type of recordable dye layer that the CD has are the most important considerations.

Reflective layer:

• A gold reflective layer is the way to go. Gold is chemically inert and won't oxidize over time, a possible risk for CD-R media with silver reflective layers.
• Consequently, gold discs are believed to offer better longevity than silver discs, although they usually sell for roughly the same price. You can purchase blank gold CD-Rs from many vendors.

Dye layer:

• The disc's dye layer, where the data is actually preserved, is equally important.
• The leading choice is phthalocyanine, a clear or light-green dye that offers the best resistance to light and heat; it is used almost exclusively with gold discs.
• Azo dye, which has a deep blue colour, is a close second. Cyanine, which has a light blue tint, is the most common and least expensive dye and is the one most susceptible to damage by sunlight and UV radiation.
• You can usually tell what type of dye is used by examining the underside of the disc — that is, the side that faces down in your player or PC disc drive.
• Note that the colour you see will be affected by material used for the disc's reflective layer. (For example, a gold reflective layer with a blue dye will appear green in colour.)

• Unless, of course, you intend to burn a lot of discs in a relatively short period of time. That's because the organic dye used to record the data on the disc will eventually spoil if it is not used.
• Although CD-R and DVD-R manufacturers claim blank, unused discs have a five-year shelf life, that claim has not been verified by independent testing, and you won't find any expiration dates on the packaging.
• All things considered, it's best to buy new discs on an as-needed basis, rather than purchasing a large quantity to use over several years.

• If you're looking to use the CDs you're buying for archival purposes, steer clear of rewritable CDs (CD-RW).
• Although they're designed specifically for data backups, CD-RWs are fundamentally different from CD-Rs: They have an aluminum reflective layer, and record data on a phase-changing metal-alloy film rather than an organic dye.
• CD-RWs are less stable, more sensitive to heat damage, and have a much shorter lifespan than CD-Rs (typically 25 years or less, depending on how many times they're recorded on).