On Thursday, September 06, 2001 at 8:56, Wayne Harridge
<olympus@xxxxxxxxxxxxxxx>
wrote on "Re: Re: Re: [OM] Re: Digital Musings," saying..
> > Tom A. Trottier <Tom@xxxxxxxxxxxxx> wrote:
>
> > CD life is ~100 years or more.
>
> Estimated ! I've never seen a 100 YO CD. I'd guess that even the substrate
> material has not been around for more than 30 years.
>
> > Film has to be very well washed to be archival.
>
> I can still print/scan from my b & w negs made 30 years ago and I have made
> contact prints from glass plates perhaps 50 YO.
>
> > B+W needs a hypo eliminator.
>
> > Color dyes are frangible by light, heat, age...
>
> Perhaps somebody with a bit more knowledge of the CD process could fill me
> in,
> but I thought that the type of CDs that you can burn on your home PC
> (compared
> with for example a mass produced music CD) were based on changing a
> dye "image" embedded in the CD.
"CD-Recorders permanently write data to special CD-R media with four
layers -- one features a light-sensitive dye layer made of cyanine,
pthalocyanine or azo. A laser is used to alter the dye to create low
reflective areas or "marks" that imitate the molded pits and lands of
a conventional CD. Unfortunately, once a CD-R disc is altered by a
laser, it's changed forever. And since burning a CD-R disc is
sometimes a tricky process, if you screw up, you have to start over
again with a new disc.
CD-ReWritable drives take the technology used by CD-R one step
further. CD-RW disc uses a phase-change alloy composed of silver,
indium, antimony and tellurium instead of a dye layer. This allows
you to rewrite over old data several times. To write data, a laser
heats the crystalline (highly reflective) phase-change alloy to its
melting point. After cooling the alloy changes into an amorphous (low-
reflective) state. To erase or write over existing data, a lower
power laser is focused on the amorphous marks to raise the alloy to a
specific temperature at which it cools back to a crystalline state, a
switch that can be made successfully thousands of times over."
See http://www.amtrakdjs.org/faq/cdrsanddyes.htm re dyes.
See http://www.cd-info.com/CDIC/Technology/CD-R/Media/Kodak.html
re lifetime.
Unfortunately, the technology may be dead by the time the estimated
217 years to the first mistake rolls around....
Tom
-------- Questions answered, answers questioned. No spam, please
Tom A. Trottier <Tom@xxxxxxxxxxxxx> ICQ:57647974 +1 613 291-1168
fax:594-5412 415-400 Slater St. Ottawa ON Canada K1R 7S7
*After 2001 Oct 20:758 Albert St, Ottawa ON Canada K1R 7V8*
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