Reading a CD that has no reflective layer
tothwolf at concentric.net
Tue Nov 18 14:12:39 CST 2014
On Tue, 18 Nov 2014, John Foust wrote:
> At 09:30 AM 11/18/2014, Mouse wrote:
>> I was speculating that, on the scales of interest here, it's
>> easier/cheaper to produce a non-smooth surface of a uniform material
>> (how pressed CDs are actually made) than to produce a smooth surface of
>> a nonuniform material (the alternative).
> I see... you're asking why CDs couldn't be made with a printing process
> (ink on paper being effectively smooth) as opposed to the non-smooth
> method of pits and lands. On one hand, it almost sounds like you've
> re-invented CD-R, where a dye gets zapped and changes its reflectivity -
> but I was surprised to read that even CD-Rs have a single spiral
> "pre-groove" pressed into the polycarbonate. You'd need a rather precise
> printing process to make tiny spots.
>> Yes, but I think the light normally used for CD reading is outside the
>> visible range. This raises the possibility that the disc might be
>> clear in the visible range but not in the range used for reading. Your
>> experience trying to read it argues against that, though. Oh well, it
>> was a nice theory while it lasted.
> At this point, I only hold out hope for finding an existing reader that
> can see the pits, and the best candidate seems to be the oldest readers,
> not the newest.
> I can't help but think this is an important topic for data recovery. A
> peeled reflective layer is a common failure mode for discs. If there
> was a way to dissolve everything above the pits (the label and aluminum)
> and recoat with acrylic for protection, and read a clear CD, you could
> rescue failed CDs.
Couldn't one also apply a layer of aluminum? This is commonly done with
mirrors for optics in telescopes and such, by hobbyists. I'm not 100%
familiar with the process, but I understand it is done in a small vacuum
chamber with some sort of electrical process to vaporize the aluminum.
I think I actually have a /very/ early Philips cd-writer drive in storage,
but it is behind a couple of large stacks of gear. It has a SCSI interface
and is about the size of a home stereo component.
I /might/ also have a Philips CM-100 on another more accessible shelf, but
it may be a few days or a week before I can have a look and see what I
have. I seem to remember the drive I have has an unusual data connector.
Does the CM-100 require a special interface card?
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