How many times have you shouted at people for putting CDs on the desk the wrong side up? You must have taught countless number of people to put the CD with the label side down to avoid getting scratches on the writing side. Well, this might come as a surprise for you (unless you already know it) - you are protecting the wrong side of the CD!
The shinny side of an optical disc is the side the data is read off by the CD or DVD player, so it seems only right and natural to protect the shinny surface from scratches by laying the CD, label side down on our desk when not in use. But that’s a big mistake. To understand why you have to understand how CDs are constructed.
CDs store data as tiny physical pits on a perfectly flat polycarbonate or plastic disc. The data is stamped on the top side of a plastic disc creating millions of pits and bumps in a spiral from the center of the disc outward. A very thin layer of reflective material, usually aluminum (copper, silver or gold on higher quality CDs), is applied to the top of the CD covering the data. This layer reflects light from the laser beam passing through the polycarbonate material allowing the stamped data to be read.
A very thin coating of lacquer is applied on top of the reflective layer to act as a sealant for the reflective foil underneath. The graphics (label) is printed on top of the lacquer layer. The reflective foil, lacquer, and graphic layers combined are only as thin as a human hair and offer little to no protection to the data beneath them.
Scratching or damaging the label side will damage the CD beyond repair. Damage which penetrates down to the reflective layer, which is dangerously close to the top, will affect the disc's readability and is not repairable. Scratches on the polycarbonate read side of the disc may cause the laser beam to be distorted during the reading process. These scratches can be repaired as long as they don't penetrate down to the encoded information. But if you damage the top, you might as well throw it away.
So which is the right way to put your CD on the desk? There is none. You shouldn’t put your discs on the desk, any side. When not in use it should go straight into the case or the CD pouch. Both sides of the disk are vulnerable to scratches and are equally damaging to the data they hold.
DVDs however offer comparatively better protection because the reflective layer is sandwiched between two polycarbonate discs, offering equal protection from either side.
The next time you see someone place a CD the “wrong-side” down, don’t get annoyed. They probably know what they are doing.
Also read: Why recordable CD/DVD does not last long?