Optical “Disk Rot”
It is increasingly apparent that optical disks may not have the shelf life originally envisioned. Even with good care some may prematurely fail due to a gradual deterioration of the recording layer. The condition manifests itself as “pinpricks” and other openings in the layer of aluminum and has been called “CD Rot” in some circles.
It’s not known how many disks will suffer this condition which is thought to be due to defective manufacture where the layer of lacquer which separates the aluminum reflective layer from the label side of the disk is applied improperly allowing air to penetrate and oxidize the aluminum.
Once billed as “virtually indestructible under normal use” CD and DVD blank manufacture techniques have diminished with the price of the media. Recall how expensive these disks were initially compared to presently.
Equally at fault may be the handling of the disk by the owner. These media are apparently much more fragile than initially believed. Manufacturers claim lifespans up to 100 years, but it’s rather difficult test this.
Most people believe that the clear underside of the CD that is the most fragile surface, 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 layer. 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 (or layers because some disks have two) is sandwiched in the middle of the disk between two layers of plastic. But this structure causes problems of its own, especially in early DVDs. The adhesive that holds the layers together degrades, making the disk unreadable at least in parts.
Users that bend a DVD to remove it from a hard-gripping case or even the drive tray are particularly susceptible for developing this problem, because flexing the disk puts strain on the adhesive.
Rewriteable CDs and DVDs, as opposed to write-once disks, should not be used for long-term storage because they have a heat-sensitive layer that decays much faster than the metal layers of other disks.
For maximum life, disks should be stored vertically and only be handled by the edges. Don’t apply labels to them, and in the case of write-once CDs, don’t write on them with anything but soft water-based or alcohol-based markers. Disks should be stored in a cool, dry place.
Tips
- Store disks upright (book style) if in cases.
- Store disks in a clean cool, dry, dark place.
- Open a recordable disk package when you are ready to record.
- Check the disk surface for obvious defects prior to recording.
- Hold disks by the outer edge or the center hole.
- Use felt-tip permanent markers to mark the label side of a CD.
- Keep disks clean. Wipe with cotton fabric in a straight line from the center of the disk toward the outer edge.
- Return disks to cases immediately after use.