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What is discoloration that follows the grain of a CD?
FrgNdTd
post Jan 26 2012, 06:10
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In advance I apologize for my lack of correct terminology. I noticed on some of the albums I own, both new and well used various spots of discoloration appear on the information side of the disc. It is incredibly subtle and seems to follow along the CD's grain or rings sometimes veering off slightly to make a larger splotch.

Despite this odd aesthetic appearance the albums play and rip fine. I'm curious if the discoloration is a result of the method used to press the CD or perhaps some sort of warping developed over time.

Thanks.
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HTS
post Jan 26 2012, 06:28
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http://en.wikipedia.org/wiki/Disc_rot

This thing?

Assuming it is then the disk itself can no longer be salvaged. The only thing to do in this case is to rip the data from it and hope that it still "rips fine" as you have luckily found for your disks. I had one album that had tiny holes and could no longer be read.

This post has been edited by db1989: Jan 28 2012, 12:53
Reason for edit: deleting pointless full quote
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FrgNdTd
post Jan 26 2012, 06:51
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I appreciate the response. I think it's possible it could be early stages of that. It's mostly towards the center of the disc. Can rot account for wavy off colored lines circling the CD?
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probedb
post Jan 26 2012, 09:19
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QUOTE (FrgNdTd @ Jan 26 2012, 05:51) *
I appreciate the response. I think it's possible it could be early stages of that. It's mostly towards the center of the disc. Can rot account for wavy off colored lines circling the CD?


I don't think what you're describing is rot. I've noticed it before but just decided it's the way the light reflects off either the plastic, bonding or metal.
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MichaelW
post Jan 26 2012, 09:53
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Is it perhaps iridescence? Rather pretty rainbow colours, doubtless caused by interference somewhere? I just looked at a disk I bought new today, and on the label side there's a set of fairly faint quasi-rings (like rings with epicycles), and on the clear side beautiful strong radial rainbows.
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FrgNdTd
post Jan 28 2012, 05:43
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QUOTE (probedb @ Jan 26 2012, 02:19) *
I don't think what you're describing is rot. I've noticed it before but just decided it's the way the light reflects off either the plastic, bonding or metal.

QUOTE (MichaelW @ Jan 26 2012, 02:53) *
Is it perhaps iridescence? Rather pretty rainbow colours, doubtless caused by interference somewhere? I just looked at a disk I bought new today, and on the label side there's a set of fairly faint quasi-rings (like rings with epicycles), and on the clear side beautiful strong radial rainbows.

I believe you're both right. I called around to some record stores and that seemed to be a general consensus. In addition to perhaps a reaction between the plastic, bonding agent, and outside variable.

This post has been edited by db1989: Jan 28 2012, 12:54
Reason for edit: shortening quotes and removing whitespace
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psycho
post Jan 28 2012, 12:18
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I have some original pressed CDs, that have some strange patterns on the data side. It looks like marble. I tried to take some pictures, but there's too much reflection and I don't have any polarization filters for my camera... I also can't seem to find such examples on the internet to show you.

Anyway, I think that this what I'm describing isn't something to worry about, since my oldest CD with such pattern is already 13 years old and it plays and rips with no problems at all.

I don't know if this pattern that I'm describing is the same as what OP tried to describe, though.


Can anyone provide some pictures of what might be the thing that OP describes and what I'm describeing? smile.gif


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Martel
post Jan 28 2012, 20:20
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I have some marble-cake-like patterns on a few brand new CDs. It does not seem to have any negative impact.


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MichaelW
post Jan 28 2012, 21:47
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On a hunch, I looked up Diffraction Grating in Wikipedia, and found this

QUOTE
Ordinary pressed CD and DVD media are every-day examples of diffraction gratings and can be used to demonstrate the effect by reflecting sunlight off them onto a white wall. This is a side effect of their manufacture, as one surface of a CD has many small pits in the plastic, arranged in a spiral; that surface has a thin layer of metal applied to make the pits more visible. The structure of a DVD is optically similar, although it may have more than one pitted surface, and all pitted surfaces are inside the disc.

In a standard pressed vinyl record when viewed from a low angle perpendicular to the grooves, a similar but less defined effect to that in a CD/DVD is seen. This is due to viewing angle (less than the critical angle of reflection of the black vinyl) and the path of the light being reflected due to this being changed by the grooves, leaving a rainbow relief pattern behind.
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FrgNdTd
post Mar 20 2012, 16:29
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Thanks!
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alanofoz
post Mar 22 2012, 12:09
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Just for fun and a bit OT try scanning a variety of CDs.


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