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 Posted:   Jun 16, 2013 - 6:43 AM   
 By:   80cionado   (Member)

Something I've noticed on some of my CD's is the following:

It was really hard to capture it on a picture, even though I outlined it, it may be difficult to see what it is. At first it looks like a perfect circle, but when you look closer there's deviations. The one I've outlined is just a small one and as you can see, there's a different color inside the not-so-perfect circle.

Here's another example I found here:

Any idea what this is? Is it normal and just something I haven't noticed before? Is it a pressing/manufacturing error? Is it harmful to the CD, like CD-rot and CD bronzing is? Or is it in fact rear-side abrasions, which I mentioned in this thread: and is described like this:

"This is a scrape causing a fogged area, neither a radial scratch nor an axial scratch.

It can result in an audible defect because it's wide enough to qualify as an axial scratch, see below. It too can be completely repaired."

If anyone could shed some light on this, that would be great.

 Posted:   Jun 16, 2013 - 7:01 AM   
 By:   Shaun Rutherford   (Member)

My Rocketeer CD looked like that from the day I bought back in 1993 (I didn't get a CD player until then, sue me). Had a kind of wavy pattern on the back that didn't look normal at all. Played fine, though!

 Posted:   Jun 16, 2013 - 7:20 AM   
 By:   Disco Stu   (Member)

I have several CDs with fogged areas but that have shiny surfaces. I assume it's an unequal solidfication of the coating, or moisture trapped in it.
From what I have seen on TV about the CD production process, CDs are spun very fast and then a plastic is poured on the surface which is spread by the centrifugal force. Since the plastig does not enter the CD surface uniformly, it might be that spiral areas build up of different structure and different opacity.
None of my CDs that have that surface have caused any problems so far. I even have a Superman box set DVD that has an area that has a flat finish, and I mean flat as in virtually no reflection. Even that DVD has played okay so far. Then again there are DVDs that cause problems with the slightest superficial scratch. DVD issues are female: there is no rule or logic to it, and they are totally predictable in their unpredictability.


 Posted:   Jun 16, 2013 - 7:28 AM   
 By:   Marlene   (Member)

One may correct me on this but I think that those clouds are shades of different aluminum / things trapped in aluminum / aluminum of differing thickness.

The reflective layer of a CD needed to reflect the laser is made out of extremely thin aluminum (most of the time). It´s a metal and metals are affected by many things when attached to something else (in case of the CD a polycarbonate layer). Just fluctuations upon manufacturing.

As long as the reflectivity is not impaired the CD should read fine. Furthermore, it should read fine forever.

P.S.: CD rot is caused by something else (the edges of the CD aren´t sealed properly -> air creeps in -> aluminum turns to aluminum oxide -> reflective layer vanishes). Aluminum foil isn´t affected by air, water or other chemicals because it´s relatively thick (it´s called 'passivation') but the reflective layer within a CD is so thin that it disappears when exposed to the elements.

 Posted:   Jun 16, 2013 - 8:16 AM   
 By:   Traveling Matt   (Member)

I have several discs like that as well, and they simply result from using cheap materials (lesser quality foil).

You should be okay if the disc plays fine. The only real concern should be player readability, as your laser may have difficulty with such discs as it ages.

 Posted:   Jun 16, 2013 - 7:37 PM   
 By:   piano632   (Member)

I've had a few CD's like that. My guess is that happens when the CD is pressed and the plastic is not cooled evenly.

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