CDs, DVDs not the indestructible gizmos we first thought
PETER SVENSSON; The Associated Press
Dan Koster was unpacking some of his more than 2,000 CDs after a move when he noticed something strange. Some of the discs, which he always took good care of, wouldn't play properly. Koster, a Web and graphic designer for Queens University of Charlotte, N.C., took one that was skipping pretty badly and held it up to the light. "I was kind of shocked to see a constellation of pinpricks, little points where the light was coming through the aluminum layer," he says. His collection was suffering from "CD rot," a gradual deterioration of the data-carrying layer.
It's not known for sure how common the blight is, but it's just one of a number of reasons that optical discs, including DVDs, might be a lot less long-lived than first thought. "We were all told that CDs were well-nigh indestructible when they were introduced in the mid-'80s," Koster says. "Companies used that in part to justify the higher price of CDs as well." He went through his collection and found that 15 percent to 20 percent of the discs, most of which were produced in the '80s, were "rotted" to some extent.
The rotting can be due to poor manufacturing, according to Jerry Hartke, who runs Media Sciences Inc., a Marlborough, Mass., laboratory that tests CDs. The aluminum layer that reflects the light of the player's laser is separated from the CD label by a thin layer of lacquer. If the manufacturer applied the lacquer improperly, air can penetrate to oxidize the aluminum, eating it up much like iron rusts in air. But in Hartke's view, it's more common that discs are rendered unreadable by poor handling by the owner.
"If people treat these discs rather harshly, or stack them, or allow them to rub against each other, this very fragile protective layer can be disturbed, allowing the atmosphere to interact with that aluminum," he says. Part of the problem is that most people believe it's the clear underside of the CD that is fragile, when in fact it's the side with the label. Scratches on the underside have to be fairly deep to cause skipping, while scratches on the top can easily penetrate to the aluminum. Even the pressure of a pen on the label side can dent the aluminum, rendering the CD unreadable.
DVDs are a bit tougher than CDs in the sense that the data layer is sandwiched in the middle of the disc between two layers of plastic. But this structure causes problems of its own, especially in early DVDs. The glue that holds the layers together can lose its grip, making the disc unreadable at least in parts.
Handling tips for CDs and DVDs
Do:
1. Handle discs by the outer edge or the center hole. Your fingerprints might be acidic enough to damage the disc.
2. Use a felt-tip permanent marker to mark the label side of a CD. The marker should be water-based or alcohol-based. In general, these will be labeled "nontoxic." Stronger solvents might eat through the thin protective layer to the data.
3. Keep discs clean. Wipe with cotton fabric in a straight line from the center of the disc toward the outer edge. If you wipe in a circle, any scratches might follow the tracks of the CD, rendering them unreadable. Use CD/DVD-cleaning detergent, isopropyl alcohol, or methanol to remove stubborn dirt.
4. Return discs to their plastic cases immediately after use.
5. Store discs upright (book style) in their cases.
6. Store discs in a cool, dry, dark place with clean air.
7. Open a recordable disc package only when you are ready to record.
8. Check the disc surface before recording.
Do not:
1. Touch the surface of the disc.
2. Bend the disc. This might cause the layers to separate.
3. Use adhesive labels, since they can warp the disc or unbalance it.
4. Expose discs to extreme heat or high humidity. Don't leave them in sun-warmed cars, for instance.
5. Expose discs to extremely rapid temperature or humidity changes.
6. Expose recordable discs to prolonged sunlight or other sources of ultraviolet light.
For CDs especially do not:
1. Scratch the label side of the disc. It's more sensitive than the transparent side.
2. Use a pen, pencil or fine-tip marker to write on the disc.
3. Try to peel off or reposition a label. Again, you risk unbalancing the disc.
SOURCE: National Institute of Standards and Technology
Shamelessly plagarized from: The Associated Press (Published 12:24AM, May 6th, 2004)
