CD Rot

As a collector of CDs and DVDs for many years (legitimate factory pressed ones), I’ve noticed that some of my older CDs have begun to have little pin-prick-sized transparent holes or dark spots in the information layer. I know this has been known to cause skipping and readability problems. However, so far, all of the discs of mine with this CD rot problem still seem to play fine.

So… obviously, I’m not complaining! What I am wondering though is… scientifically, how is this possible? If there is physical damage to the part of the disc where the data is stored… how do the affected areas still play?

The reason your discs still play is that all CDs have error correction, and you can have defects up to a certain size before the error correction becomes unable to correct all data. When this happens on an Audio CD in your CD player, the player will start interpolating (guessing) the missing values and you might not be able to hear the difference. When the defects become too large this will start to sound bad and as the defect increases in size you won’t be able to play the disc at all.

I suggest you start making backups of any CD that has these pinprick holes. If you buy some 2CD jewel-cases, you will be able to keep both the original CD and the backup in the same jewel-case - this is what I have done for the few such discs that I have.

I have some very old audio CDs and have never experienced that problem.

I used to always get this with about 5-6 years ago with ALL pthalocyanine CDRs. That’s why I only use verbatim or TY media. Ritek Pthalo seems alright tho

You could say that about any statistic. But when you don’t have “some” and instead have “a lot”, the increased sample size will reveal more accurate statistics.

As for how they can develop pin-prick holes? well it’s places where the protective lacquer that prevents moisture and oxygen from oxidising the thin aluminium layer has worn or not correctly applied or broken down due to light, heat or ageing which is due to poor chemical construction. When the layer is broken, the reflective coat of aluminum is exposed to the air and moisture, oxidising and corroding the thin coat of aluminium away developing a dark spot, or a complete hole which grows over time. Yes BACKUP while error correction can still take care of it - because there’s always a limit to how much you can recover once the rot becomes extensive.