From: bill@bilver.uucp (Bill Vermillion)
Subject: Re: CD rot --- actually known as Laser Rot (It exists!)
Organization: W. J. Vermillion - Winter Park, FL
Distribution: usa
Date: Sun, 12 Apr 1992 16:49:39 GMT

In article <1992Apr06.055042.1427@mixcom.com> ray.chramega@mixcom.mixcom.com (ray.chramega) writes:
>
>
>Sorry if this duplicates something you've already posted. I'll admit I
>haven't read all the posts in the subject of CD rot.

>Apparently in the early days of laserdiscs (1978 or so is when I first
>saw them go on sale), discs were manufactured with two chemical agents
>that didn't react well together. The supervisor named these two 
>ingredients by name, but I've forgotten what they were. Anyway, disks
>haven't used those chemicals since way back then. I was told that any
>discs I buy today won't rot, except if I happen to buy an older disc
>from a dealer of used laserdiscs of course.

Well it is not always interaction between the layers.
Sometimes it is that the layers do not get sealed properly, and
air will leak in.   Aluminum oxidizes very rapidly - while
polished unoxidized aluminum relflects well, oxidized aluminum
does not.

>
>Laser rot is a black circlular formation that will appear on a disc
>after continued use. Once it occurs it just starts growing and growing
>everytime you play it.

This is not always the case.  I have a disk that has little
circles growing on.   Looks like a mold spore from something
that was on the disk surface before gluing together.  Many
instances of laser rot are not visible at all to the naked eye.

>I have one disc in my collection I did buy from
>a used laserdisc store. I bought it knowing it had early stages of
>laser rot. The disc sounds horrible and is very fuzzy and crackles
>terribly. The disc is "The Making of Star Wars". The only way to deal
>with this problem is to watch it seldomly, and never pause it with the
>picture on the screen. Or else the laser burn grows larger.

The disk rot is an atmospheric event.  It will continue whether
or not you watch the disk, play the disk, or pause the disk.
Laser in cd/ld players are of such low power they will not burn
anything or harm the disk in anyway.

I am lucky in that I have laser rot on only a very few of my
disks.  The problem is that the one disk that has the most
severe case is non-replaceable.    By going to the analog audio
track, the audio clears up, and I can watch the version with
the noise - but it is irritating.

>
>Joke or not... Laser rot did exist! but only in laserdiscs. CDs weren't
>available in 1978. So you don't have to worry about CDs at all.

The reason you don't have to worry about CDs is that it is a
lacquer coating applied to the disk, not another platter that
is glued to the disk.  There are a few LDs being made as CDs -
the Warner Brothers sampler immediately comes to  mind.
Thickness of a CD and a screen label on the other side.  It's
just a big CD with pictures :-)

The image catalog, also an 8" thin disk does have two sides. It
is not glued together.    I suspect it may be from a two side
mold and laquered on both sides.   I do not have any tech specs
on this disk, but it is also of the 8" single LD as opposed to
the original 8" music video LDs that were standard thickness.

If you are not familiar with these, the original LD players
could not handle the thin disks and need an 8" adaptor disk to
make up for the thickness so the clamping ring will grap the
disk.

>
>Hope this answers some questions.


-- 
Bill Vermillion - bill@bilver.uucp 
                - ..!{peora|ge-dab|tous|tarpit}!bilver!bill