> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:[log in to unmask]] On Behalf Of Konrad Strauss
> Sent: Wednesday, February 23, 2005 7:56 PM
> To: [log in to unmask]
> Subject: Re: [ARSCLIST] Audio storage on external hard drives
>
> on 2/23/05 6:31 PM, John Poirier at [log in to unmask] wrote:
>
> > supporting the widely held perception that "gold dye" CDs are likely to
> > survive aging much better than other types. Non-gold discs appear to be
> not
> > only shorter-lived than gold dye but frequently outright lousy.
>
> This is a widely-held misunderstanding of CD-Rs. I'm sure that Jerry will
> be
> able to chime in here in with more details, but there is no such thing as
> gold dye discs, what you are seeing is the gold reflective surface
> underneath the dye. Gold is considered to be more archival because it does
> not tarnish like silver or aluminum when exposed to oxygen. There are 2
> basic dye types, Phthalocyanine and cyanine. Phthalocyanine is clear to
> the
> eye, the disc appears to be the color of the reflective surface -
> therefore
> the impression of the gold dye discs. Cyanine dye can vary from green to
> blue in color, therefore the impression of green or blue dye discs.
>
> Now for the nitty gritty. Generally speaking, cyanine dye works with a
> wider
> range of laser power and tends to be more compatible, especially with
> legacy
> burners. But it is sensitive to UV and can degrade if exposed to sunlight.
> Phthalocyanine dye requires tighter control of laser power when burning
> and
> can exhibit compatibility problems with certain burners. But it is not
> sensitive to UV and is considered to be more archival. But there's more.
> The
> CD burner is also a major part of the equation. Since dye formulations are
> changing all the time, and as blanks become optimized for higher speed
> burning, and as burners are capable of ever faster burning speeds, legacy
> burners can slowly become incompatible with CDR blanks. Additionally,
> burners do wear out - they have a limited lifespan and after a certain
> number of discs the laser will no longer be able to calibrate itself to
> the
> current generation of blanks therefore increasing the error rate.
>
> So, just because a certain burner/CDR combination produced acceptable
> discs
> in the past does not mean that it will continue to do so. As Jerry often
> points out, regular testing is a necessary part of any archival CDR
> operation. Mastering engineers, who are truly anal retentive about error
> rate test every single disc they make. In fact, most mastering engineers
> use
> cyanine discs because they tend to produce a lower error rate. Tayo Yuden
> seems to be the preferred brand.
>
> --
> Konrad Strauss
> Director of Recording Arts
> Associate Professor of Music
> Indiana University School of Music
> http://php.indiana.edu/~kstrauss
> http://www.music.indiana.edu/department/audio/

See http://www.mscience.com/faq.html for our well-known position on media
"color". Simply put, it is not relevant when compared to many other factors
including pregroove quality, the writer, and handling and storage.

Does anyone have solid data showing that CD's are especially sensitive to
UV? I see this mentioned rather frequently, but without supporting data.
CD's are sensitive to IR, since that is the wavelength used for recording.

I believe that cyanine recording changes the polymer structure of the dye,
while phthalocyanine recording causes local melting. Any source of absorbed
radiation can raise the overall temperature of the dye, causing degradation
if intensity levels are sufficiently high.

NIST ran tests with high levels of near IR and visible light, but I suspect
that much of the results were related to heating rather than by the
radiation itself. The CD-R samples were mounted on a temperature-controlled
plate, but were not thermally bonded to it.

Last but not least, http://www.mscience.com/longev.html reports that
unrecorded discs are affected more by high temperature/high humidity storage
than are recorded discs.

Jerry
Media Sciences, Inc.