It is a myth that CDs can be dirty, scratched, marred and still play. Scratches, dust, dirt, fingerprints, and warping can effect CD sound quality. Here are some tips to deal with these inevitable problems.
CDs are made from polycarbonate plastic and like any plastic the surface is subject to scratches. A few scratches are not bad since the player has an error circuit that will compensate for some scratches. However there are two kinds of scratches that can occur that can have differing affects.
A radial scratch (see diagram) on the bottom (play) side of the disk will pose the least amount of problems if it is around 1mm wide and does not dig too deeply into the surface.
However, if the scratch is parallel (see diagram) to the edge of the disk, there may be more information lost and the audio output may pop or skip. In any case, the deeper the scratch is, the more likely it will be that an audible error will occur.
Scratches to the top (label) side can prove to be the worst. The plastic coating on the top is very thin and even a shallow scratch can cause damage to the aluminum stamping under the label. This area contains the digital information and if damaged, is not replaceable or repairable, thus ruining the disk.
For the best sound quality, a disk should be free of fingerprints as they can affect its playability. The CD system works by reflecting laser light and skin oil is partially reflective. Fingerprint oil will reflect the laser light back to the photodetectors before it reaches the aluminum stamping. This will cause lost data or a weak signal. Both of these things will cause mistracking, loss of sound quality and other errors. (see cleaning instructions)
Always, when handling the disk remember to hold it only by the unencoded edge or by placing a finger in the central hole.
Small amounts of dirt and dust are invisible to the CD player and a small accumulation of these won’t noticeably affect your CDs. But remember, where there is even a small amount of dirt and dust, there exists the potential for causing scratches. The best preventive medicine is to always keep your disks in their jewel cases when not in use and to keep them free of fingerprints that can trap dirt.
To put it simply, a warped disk will not play. Any warpage beyond that which occurs during manufacture, will cause the disk to fail due to the close tolerance of the optical pickup.
In some instances however, warping can be eliminated so do not discard it outright. To check for warping, place the disk on a mirror or piece of window glass and check for gaps around the edge of the disk.
If there is any dirt and/or dust present, improper cleaning can scratch your disks. Also, do not clean CDs unless a patron complains about it. You should never wipe the surface with your finger or with a dry cloth. Your finger, no matter how clean you may think it is, will leave an oil deposit on the surface (see Fingerprints). A dry cloth, like your shirt or the leg of your pants, may just trap the dirt particles and grind them into the surface, causing scratches.
The best way to clean a CD is to first squirt the bottom surface with a can of compressed air to remove any loose dirt and dust from the surface. After doing this, further cleaning may be unnecessary.
If further cleaning is still necessary follow these simple rules. There are special CD wipes available that are ideal for this. If you are in a situation where these are not available, use only a cloth that is lint-free. The industry standard however is not to use a cloth but instead to use a chamois or a soft, clean sponge material like a sponge Q-Tip.
When wiping a CD, wipe from the inside hole to the outer edge in a straight line (see diagram below). Never wipe in a circular motion or around the circumference of the disk. Fingerprints and heavy grime may require more wiping but avoid using too much pressure.
Avoid cleaning the top surface if you can. Even if there are fingerprints, etc., on the top, these will not affect the sound quality of the CD. The plastic coating on the top of the CD is shallow and even a light cleaning may scratch through the coating and damage the aluminum stamping under the label. If the aluminum stamping is marred, the CD is ruined.
Eric Shardlow, Fresno County Library