CD rot

 

I have had 2 HD failures so far.

 

Thats why I thought it worth a mention.

 

oxidisation you say...this can only happen in the presence of oxygen. Perhaps we are going to have to keep our original cd's in vaccums, while we have a backup collection of copies for everyday play. There are also sealants that can suppress oxidisation. I wonder if they can be incorporated into future cds, if they're still around then!

 

yeah, it's obvious that music is going digital, but I like having that physical tangibility that comes with cds. I wish they'd just make quality cd's or some other tangible disk. I guess i'd be just as happy if they packaged cd's just as they do, but there's a computer chip inside or something and they made radios that'd play em'. Yeah, I know they'll never spend any extra money of dealing with the problem.

 

 

As a point of information. A CD consists typical of ~1mm of polycarbonate encoded with  laser readable pits, which are aluminised with ~ 70nm of pure aluminium (I've been told by my local metallurgists), and this is in turn is coated with an acrylic based lacquer, which will then have the individual info printed on it. So called audiophile discs have gold instead of aluminium deposited (but do your sums, at 70nm by 5 inch diameter, how can they justify doubling the price of the CD?). Rot is either oxidation or hydrolysis of the aluminium layer i.e. pure aluminium can't survive in earth's atmosphere without forming a protective oxide or hydroxide layer which then protects the underlaying aluminium metal. Aluminium oxide is white and larger volume than its parent metal hence the acrylic coating with the contaminated aluminium are forced off the polycarbonate. Rot is proabably due to oxygen or moisture permeation through a few tens of microns of lacquer, getting at the aluminium layer: this was reported to be the  main problem. However, the CD manufacturers did claim well over a decade ago, they were using or moving to non-permeable lacquers. In some instances way back, the centre hole of a CD was punched out exposing the aluminium to the environment. Chromium is not used since potentially it is an environmental pollutant, silver is far too expensive - besides gold is used already.

 

Do it yourself burn CDs were claimed to have a 2 year life, a decade ago, especially if you didn't store the CD in a box and let it get exposed to sunlight - apparently UV damages the coating, which reacts with the laser burning treatment to give the pit encoding. However, compilations I burnt in 1994 are completely playable - maybe this was a con to get you to keep copying CDs, hence buying more burnable CDs!