Actually Bigdog, while you are "technically" correct in your "sandwich" comment, it's not strictly speaking, correct.Bigdog wrote:The aluminum foil sandwiched in the plastic of the music disks was not put there in a clean environment..,..the aluminum foil became infected with oxidation particles....look at your aluminum screen door... That's oxidation....It's occurring inside each and ever disk...I have SOUND CHOICE discs that look like swiss cheese when you hold them up to the light...so even in a drawer not being used they could disappear....
Technically they said CDs would last 50 years....Not so....now if the foil was gold...It would last forever...except for external scratches on the plastic...
Surprisingly, CD's are produced in very much the same way as a vinyl record by initially pressing from a "Master" copy.
Thereafter, it changes dramatically in how the Aluminium (note the correct spelling of Aluminium, by the way for the benefit of my American cousins layer is produced.
The layer is vapour deposited on the Polycarbonate substrate in Vacuum, therefore in the total absence of Oxygen, so NO Oxide on the front surface is possible.
A micro-thin laquer coat is then immediately applied to the back of the disc, then any artwork is silk-screend on.
Please note and trust me on it, this is INVARIABLY done in a clean room of some description.
There are two main causes of CD damage;
1) bad handling damaging the BACK coating of the CD that is very thin and can't be easily repaired, while the front, much thicker layer, CAN be filled with suitable refractive index plastic, or polished.
2) the one that will hurt every KJ and Dj's feelings most, simply pausing a disc for extended periods when cuing up a track.
People don't appear to understand that a Laser, even a low power CD Laser is a HIGH ENERGY beam of light and will heat up anything it strikes.
When you cue a track up, all that happens is the Laser is switched off for one revolution and switched back on when it hits the cued up portion of the selected track, many times a second for as long as the CD is paused.
Result, that one spot gets hotter and hotter, 'till eventually the Aluminium burns away, leaving a visible hole.
If you don't believe me, play a CD all the way through then immediately take it out of the drive. You'll find it's pretty damn warm, I betcha.
In theory, assuming the BACK coating is sound, it is IMPOSSIBLE for the Aluminium layer to Oxidise, basically EVER.