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Re: [ARSCLIST] Replating CDs
Clarifying my terminology:
Don Cox wrote:
>> To properly re-coat an existing CD you'd need to remove the original
>> label ink, lacquer and reflective coating, then prep the surface in a
>> way that allowed the new coating to adhere properly
>
AFAIK there is no "prep" of the polycarbonate before the metal is
evaporated onto it. It has only to be clean.
I'm talking about preparing a CD for *re*-metallizing here, not the
process of creating a new CD. Even if you can remove everything from
the surface -- down to the bare polycarbonate -- that surface may still
not have the exact same physical characteristics that it had when the
disc was fresh out of the mold, and might therefore require additional
surface treatment before another reflective layer is applied.
I'd want to try the IRENE approach first: find a way to
directly image the pits from the "clear" side of the disc and
reconstruct the encoded data from that.
That is what any CD player does. We are talking about valuable discs
that cannot be read in the normal way, because the reflecting layer is
damaged.
CD players calculate pit size based on the length of time between
changes in the intensity of the laser light bouncing off the reflective
surface. I'm talking about taking photographic images of the pits/lands
under high magnification and measuring them from those images -- hence
the reference to IRENE. This technique might also work for recordable
discs that are too badly damaged to be read by a standard player,
depending on the nature and amount of that damage.
(A similar system might be possible for magnetic tape, replacing the
photographic imager with a high-density array of magnetic detectors.
These could be passed over the tape surface to create a two-dimensional
"map" of the surface's magnetic properties, which could be analyzed in
software to decode its content. A device like this theoretically could
read magtape in any obsolete format, provided the tape's structurally
sound enough to allow it.)
that process still poses less risk to the actual data than trying to
>> chisel any remaining metal out of the pits themselves.
I said nothing about chiseling. The process would use a chemical solvent
and possibly ultrasonics.
Read "chisel" as "remove via means involving a physical/mechanical
process". Again, any process requiring direct physical interaction with
the pit surface of the disc has some risk of damaging that surface.
There are a number of possible methods for reading that information from
the other side of the CD, none of which have that risk, and which
therefore would be better first approaches than re-metallization.