Reading a CD that has no reflective layer

Tothwolf tothwolf at
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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