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If you are referring to CD-R in your first paragraph, then I would agree
with you, especially if ageing is conducted at an unrealistically high
temperature of 80 degC (far in excess of the maximum specified in the Orange
Book.) Accelerated ageing tests conducted at realistic 60 degC and 85% RH by
Media Sciences show wide variations.

Cyanine/silver discs may be superior or terrible. Phthalocyanine/gold discs
may be very good or awful. It all depends on the process design and control
by the manufacturer. An older study by NIST concluded that
phthalocyanine/gold was superior while ignoring test results published in
the same paper showing that one phthalocyanine/gold brand (unnamed) gave the
worst results of all dye/metal combinations.

What needs to be added to the discussion is as-recorded quality. A very high
quality disc that ages gracefully is preferably to a poor quality disc that
is very stable. My point is that blindly relying on a single dye/metal
combination can lead to unsatisfactory results.

Jerry Hartke
Media Sciences, Inc.

> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:[log in to unmask]] On Behalf Of [log in to unmask]
> Sent: Monday, December 08, 2008 10:04 AM
> To: [log in to unmask]
> Subject: Re: [ARSCLIST] DVD-R recommendations?
> 
> Testing has shown that phthalocyanine dye and gold metal layer results in
> the most stable discs. The testing involved accelerated aging. That being
> said, I would have more confidence in media that survives this torture
> test
> as opposed to media that does not and that is about all you can say with
> confidence. Accelerated aging is what it is - a tool to make predictions
> in
> order to provide reasonable advice. The actual numbers are not really all
> that important, but comparing the numbers is much more useful in the
> decision making process.
> 
> DVD-Rs do not use phthalocyanine dye. Some gold metal layer DVD-Rs are
> available. In light of the serious metal layer corrosion that I have
> observed in DVDs from testing, I believe that using a gold metal layer is
> the necessary choice when longevity is the issue. I will have to disagree
> with Jerry on this one. The metal layer integrity is one of the most
> important factors in disc longevity. Having a chemically stable metal
> layer
> eliminates a critical degradation pathway.
> 
> Gold metal layered media can be recorded to low error rates. Silver metal
> layer discs tend to have better compatibility because of the higher
> reflectivity of the metal layer, although I have had few problems with
> gold
> metal layered discs.
> 
> Gold metal layer, moderate writing speed, and good disc recorder
> compatibility will give you the best disc for longevity.
> 
> The Kodak discs now being sold are rebranded MAM discs which have
> performed
> very well in accelerated aging tests compared to other media.
> 
> 
> Joe Iraci
> Senior Conservation Scientist
> Canadian Conservation Institute
> 1030 Innes Road
> Ottawa, Ontario, Canada
> K1A 0M5
> (613) 998-3721 ext. 142
> www.cci-icc.gc.ca