Reading a CD that has no reflective layer

John Foust jfoust at
Tue Nov 18 09:48:25 CST 2014

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.

- John

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