W. Cardone Productions Blog

CDs or DVDs do not require routine cleaning. It is best to clean the disc only when it is absolutely necessary, specifically:

• before storing, when surface contamination is visible
• before recording, when surface contamination is visible
• before playing, to prevent surface contamination from being “flung off” while the disc is spinning in the disc drive
• when readability (playability) is impaired and surface contamina-tion is visible

In general, avoid using organic solvents. Harsher solvents (ac-etone, benzene) will dissolve the polycarbonate and damage the disc beyond repair. Mild solvents (isopropyl alcohol, methanol), however, may be used. These mild solvents evaporate quickly and will not disthe polycarbonate.

Other solutions that are not harmful are water-based lens clean-ers or water-based detergents (with mild soap) formulated for clean-ing CDs or DVDs.

The polycarbonate substrate is a relatively soft and transparent type of plastic. Each time a disc is wiped, rubbed, treated with some solution, or otherwise manipulated for cleaning, that substrate, and thus the disc itself, is at risk of scratching or contamination.

If the disc needs cleaning, remember these tips:

• Use an air puffer to blow off dust.
• Use a soft cotton cloth or chamois to wipe the disc.
• Try cleaning with a dry cloth first, before using any cleaning solutions.
• Do not wipe in a direction going around the disc.
• Wipe from the center of the disc straight toward the outer edge.
• Avoid using paper products, including lens paper, to wipe the disc.
• Avoid using anything abrasive on the surface of the disc.
• If the disc has a heavy accumulation of dirt, try rinsing it with wa-ter first.
• Use commercially available water-based detergent formulated for cleaning the surface of optical discs.
• Use isopropyl alcohol or methanol, as an alternate to water-based detergents, to clean the disc surface.

Scratches on the Laser-Reading Side of CDs and DVDs
Scratches generally cross data lines or tracks on the disc, and how bad (deep and wide) they are will determine the extent of interference with laser focus on the data. Small or occasional scratches will likely have little or no effect on the ability of the laser to read the disc, because the data are far enough below the surface of the disc that the laser is focused beyond the scratch. This is comparable to the effect of a light scratch on a pair of eyeglasses; it does not markedly impair vision because the viewer’s eyes are focused beyond it.

Even assuming a scratch is deep or wide enough to influence laser focus, error detection and correction coding in the disc drive can in many cases recover the misread data. However, scratches that are deep, wide, or bunched together can adversely affect the readability of the disc. These scratches can cause the laser to misread enough data to make error correction coding ineffectual.

While data errors generated from scratches that run outward from the center of the disc stand a good chance of correction by the error correction firmware, scratches running in the direction of the track, the same direction as the laser reads the disc, are more likely to cause uncorrectable errors. If scratches are deep enough to damage the data or metal layers on the reading side of a disc, the data cannot be read or repaired.

Scratches on the Label Side of CDs
Scratches on the label side of discs can be a more serious problem. Because the reflective metal layer and data layer are so close to the surface of the label side of the disc, they can be damaged very easily. A slight indentation, or pinhole in the metal from a scratch, pen, pencil, ultrafine marker, or other sharp object will destroy the reflectivity of the metal in that area on the other side (laser reading side) and the readability of the data by the laser. This type of damage cannot be repaired.

As with scratches on the laser-reading side, optical disc drives are usually able to read through minor damage easily, even if the damage is caused from the label side. The difference is that this damage is permanent. If the error detection and correction firmware in the disc drive cannot correct the data, it will not be recoverable. Scratches that do not reach through the thin protective lacquer coating should have no immediate effect but may ultimately expose the metal to moisture, air pollutants, or other adverse environmental influences.

Adhesive labels, though also somewhat vulnerable to adverse environmental influences, can provide CDs with extra protection from scratches. The extra layer on printable discs likewise offers protection.

Scratches on the Label Side of Single-Sided DVDs
Scratches on the label side of single-sided DVDs are not likely to pose a problem. The metal layer so prone to damage in CDs is in the middle of DVDs. Its location makes this layer almost impervious to surface scratches; it is in fact unlikely to be affected by any but the deepest scratches—those deep enough to reach the center of the disc where the metal and data lie.

Adhesive labels should not be applied to optical discs destined for long-term storage (more than five years). The label could delaminate over time and interfere with disc drive operation. The adhesive in some earlier labels has also been known to react with the lacquer surface. Any attempts to peel the label off could cause damage to the lacquer and metal layers in CDs. DVDs are different; peeling a label off a DVD would not have the same adverse affect because the metal layer is not near the surface. Still, removing a label, or any portion thereof, from the surface of a disc can cause an imbalance in the spin of the disc in the disc drive, making the disc unreadable. DVDs are more susceptible to reading problems from minor imbalances than are CDs. To ensure the long-term availability of information on a disc that already has an adhesive label, the information on the disc should be copied to, and stored on, a disc without such a label.

Adhesive labels may be well suited for short-term disc usage (less than five years), and can even add a layer of protection from scratches and other potentially harmful contact. On the other hand, such labels are vulnerable to adverse environmental conditions: they can dry out or absorb moisture, and they can be affected by heat or cold even more than the disc itself. Such conditions may cause the label to delaminate. Disc manufacturers advise against using adhesive labels because they can create unbalanced disc spin, resulting in premature wear of the drive. If a label is used, it should be manufactured for use on CDs or DVDs, and an appropriate disc label applicator tool should be used to affix the label. The label applicator tool should center the label on the disc so as to maintain the disc balance as much as possible.