Thursday, September 14, 2006

Providing Care and Protection for Optical Discs

Most of us use some kind of optical disc in our daily activities, such as CDs (compact discs), CD-ROMs (compact disc read-only memory), CDIs (compact discs interactive), DVDs (digital video discs), and soon-to-come Blue Ray storage discs. These are all optical media that use laser beams to read information for data retrieval.

Each of these media has a clear coating that protects the discs’ data section. When scratches occur, the damage is not to the actual data section; rather, the damage is to the clear coating. The best way to repair a damaged disc is to polish down the scratches to remove them.

Lasers write to only one side of a CD whereas a DVD can be written and read from both sides. Unlike vinyl records or tapes, CDs and DVDs do not wear from friction because there is no physical contact with the disc in the area that the laser accesses, and there is no degradation of magnetic storage. CDs and DVDs are durable media and have a long life expectancy if they are handled carefully.

Extending a Disc’s Life
• Handle CDs and DVDs carefully, generally by the edges or the hold to avoid touching the shiny surface (signal side) since finger prints, smudges, or scratches attract dust and moisture that interferes with the laser reading the disc’s data
• Keep discs in a cooler and lower humidity environment
• Protect discs from airborne contaminants by housing them in individual storage containers and stored upright to prevent bending
• Avoid writing on the disc with a sharp pen, pencil, marker and avoid using affixing adhesive labels

Cleaning a Disc
• Blow off dust by using an air puffer
• Use a soft cotton cloth to wipe a disc, wiping from the center straight to the outer edge and not in a circular pattern around the disc
• Avoid touching the disc with paper products such as lens papers or with abrasive products or solvents to clean the disc
• Remove a heavy accumulation of dirt by first rinsing the disc with water

Handling Scratches
• First inspect your disc, cleaning it so you can see where the scratches are. Holding the disc by its edges, wash it with mild soap and water and then examine the disc under good light. Slight scratches will most likely have little effect on the laser’s ability to read the disc. Large scratches, however, can affect the disc’s readability beyond the ability for error correction. If scratches are very deep, data cannot be read or repaired.
• Scratches on the label side of the CD can be serious. Any slight indentation or pinhole in the metal from a scratch, pen, pencil, or fine marker will destroy reflectivity of the metal in that area on the other (laser reading) side, and this damage cannot be repaired.
• If problems persist when trying to play the media, check the disc player to determine if the laser reader is working properly or if the lens needs to be cleaned.

In Bracken Library’s Educational Resources Center, we use Paulmar’s CD/DVD polisher to eliminate severe surface scratches on discs that interfere with playback, allowing us to save many damaged discs that would otherwise have to be discarded.


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