I've written previously about the damage the wrong pen or marker can do to your CDs and DVDs. But really, the biggest danger to the long-term health of your discs is the media itself -- some discs are just more reliable than others, made with better materials, equipment and quality control processes. A couple years ago, the UK Independent published an illuminating article on CD longevity, citing studies where media became unreadable after just two years in a dark cupboard -- even without exposure to sunlight or humidity, the usual culprits in CD degradation.
While some disc formats are better than others (RW discs tend to have lower rated lifespans, for example), the bottom line is that no CD or DVD lasts forever, and the professional archivists responsible for major CD and DVD collections use only top-quality media, make multiple copies, check them every few years, and recopy as needed.
So what are the best strategies for home users looking to preserve family photos or financial information? I asked Verbatim spokesperson Andy Marken for advice. He recommends looking for special "archival-grade" discs, and burning, handling and storing them with care. Archival discs are available from most of the major CD and DVD manufacturers, and may include special hardened outer coatings, more stable dye layers, and oxidation-resistant reflective metal layers. All of these things add to the cost of the disc, but are worth it when it comes to storing your most valuable data.
Interestingly, when I asked Andy whether he'd recommend DVD-R or +R media, and single or dual-layer, he said that while there isn't much difference between R and +R, "Conventional wisdom recommends that you use single-layer as opposed to double-layer media just because you are multiplying the chances for issues." The Sony Studios library, for example, divides up its video files and spans them across multiple single-layer DVDs. (Both Easy Media Creator and Toast can perform disc spanning automatically.)
Andy also wrote a great article for Audioholics about the longevity issue that ends with some dos and don'ts for CD and DVD handling:
* Handle discs by the outer edge or the center hole
* Use a non solvent-based felt-tip permanent marker to mark the label side of the disc
* Keep dirt or other foreign matter from the disc
* Store discs upright (book style) in original jewel cases that are specified for CDs and DVDs
* Return discs to their jewel cases immediately after use
* Leave discs in their spindle or jewel case to minimize the effects of environmental changes
* Remove the shrink wrap only when you are ready to record data on the disc
* Store in a cool, dry, dark environment in which the air is clean -- relative humidity should be in the range of 20% - 50% and temperature in the range of 4°C - 20°C
* Remove dirt, foreign material, fingerprints, smudges, and liquids by wiping with a clean cotton fabric in a straight line from the center of the disc toward the outer edge
* Use deionized (best), distilled or soft tap water to clean your discs. For tough problems use diluted dish detergent or rubbing alcohol. Rinse and dry thoroughly with a lint-free cloth or photo lens tissue
* Check the disc surface before recording.
* Touch the surface of the disc
* Bend the disc
* Store discs horizontally for a long time (years)
* Open a recordable optical disc package if you are not ready to record
* Expose discs to extreme heat or high humidity or rapid changes in temperature or humidity
* Expose recordable discs to prolonged sunlight or other sources of UV light
* Write or mark in the data area of the disc (area where the laser "reads")
* Clean in a circular direction around the disc.