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CD Life - was Film vs CD Revisited - LONG EMAIL



I unfortunately do not have time to discuss this topic in depth in this forum - but there has been a great deal of research lately that strongly questions the notion that CD-R media will have anywhere near a lifetime of 100 years. There are many aspects of this discussion - but for a quick start, I would like to refer those interested to a paper by Media Sciences.
 
http://www.mscience.com/survey.html
 
A paragraph in the summary states:

Readability in a few drives does not confirm quality. Even reliance upon brand name can be ineffective unless each manufacturing location and product type is qualified and regularly monitored to assure consistency. Only in-depth testing can qualify media and assure interchange and longevity. The expense of such an effort is quickly repaid when recording processes flow smoothly and field failures are minimized. Establishment of a quality baseline enables further cost savings to be achieved by reducing the frequency of testing while maintaining a high level of confidence in the process.

I suggest that you read the paper in full - it is quite revealing. The author Jerome L. Hartke is not alone in his findings. In the JTS Conference in January 2000 in Paris several papers presented examined CD-R media failure for a variety of reasons, and found that there is great and justifyable reason for concern on a nunber of fronts.  The proceedings can be ordered at:

http://www.cst.fr/jts2000/en/index.htm#actes

and worth every franc.

Still other concerns have been voiced on the AV Media Matters listserve (instructions on how to subscribe to this list are below my signature)  relating to deterioration relating to permeability. The archive of AV Media Matters can be searched at Walter Henry's excellent Conservation On Line site:

http://palimpsest.stanford.edu/byform/mailing-lists/av/

for AV Media Matters Archive or in general

http://palimpsest.stanford.edu/

where one can find many postings on this very issue.

There were several postings on permeability problems which point to long term increase in error rates which can make a CD-R unreadable

 - one in particular I quote in full from Mr. Ed Zwaneveld which sprang from a discussion regarding CD Polishing and it's ability (or lack thereof) to recover damaged media:

Greetings,

One of our CD polishing discussion partners last week, dismissed the

permeability issue of polycarbonate substrates that are used for optical

compact disc media, implying that a 10 minute inundation with water will do

no harm because he has never seen it to do harm. While respecting his point

of view, I would like to quote Dr. Martin Dubs, Optical Storage R&D Manager

of Balzers Process Systems (BPS), serendipitously writing in Medialine of

June 2000, p.38, in an article entitled: "Sputtering Configurations for

Super Audio CD (SACD) Hybrid." I just happened to receive the publication

yesterday. In his article, Dr. Dubs reports on the production process for

this newest of CD-based product and the manufacturing decisions that have

been made by Philips ODTC (the primary patent holder of CD) and its partners

Sonopress and Balzers Process System (BPS). BPS has been Philips sputtering

partner throughout the development of the SACD. The COMET metallizing system

is used for the production of both the reflective and semi-reflective layers

of the SACD. It is BPS's DVD-9 metallizing platform (state-of-the-art), and

their CUBE UNO is used to (please note) "sputter the functional humidity

barrier layer". Actually, three metallizers are applied, each metallizer has

a specific function. The SWIVEL is used for the silver, reflective layer;

CUBE LITE is used for the silicon-based material of the semi-reflective HD

layer; CUBE UNO is used for the silicon-based compound for the "humidity

protection layer". Explaining the purpose for this CUBE UNO layer, he

states: CUBE UNO provides a layer of silicon-based compound, different from

that of the semi-reflective layer, which prevents post-production warping

caused by water absorption. Precisely defined, deformation of the Hybrid

disc occurs where there are uneven rates of absorption and evaporation of

ambient humidity within the disc substrate. If the water uptake and release

are kept in balance, then deformation does not occur. The water absorption

characteristics are determined by the substrate material. Sonopress produces

on a base of polycarbonate which is sensitive to water absorption. The

problem emerges because the backside is protected by a silver layer plus a

lacquer layer while the front-side is left unprotected. Thus the substrate

experiences an uneven absorption and evaporation rate between the front-side

and the back-side. Front-side coating is necessary to stabilize the

substrate against fluctuations in humidity. The protective layer is

reactively sputtered at a 10-15 micron thickness"..."Without CUBE UNO,

warping occurs every time", asserts Sonopress' Schaper. (and they should

know.)

The question might be asked as to why this newest CD product has such a

humidity barrier layer in it, while this is not the case with any other CD

products.

The answer lies in the purpose for which this disc has been designed, which

includes high on the list, the archiving of audio.

In their technical specifications of the SACD, entitled: "Super Audio

Compact Disc-A Technical Proposal", by Philips and Sony, dated April 1999,

under the heading "Digital Stream Digital (DSD) in Archiving", Philips/Sony

list Archiving first under their requirements for the next generation of CD:

Music companies count as their assets the musical heritage of over 100 years

of recording. These include fragile, ancient acetates and lacquers plus

hundreds of thousands of reels of audio tape. All these media have a finite

archival life. For example, tape manufacturers typically specify 30 years

life. This suggests that the master tapes from the 50's and 60's require

immediate transfer onto some newer, more durable medium. Because these

precious masters may not be able to tolerate more than a single playback,

today's archival copy must capture "all of the original recording, down to

the merest hint of harmonics, buried in noise. The technology behind the

Suepr Audio Compact Disc must support such ultra-high quality archiving."

The original Compact Disc Design engineers calculated that it might take as

long as 30 years for humidity and other pollutants to penetrate through the

polycarbonate substrate in temperate climates. This implies that in tropical

climates optical CD life expectancy (LE) will be a fraction of that, and

when the disc is exposed to water or solvents that also will reduce the time

needed to permeate and harm the information/reflective layers. In addition,

as stated before, warping will occur 'every time'. Therefore, immediate harm

will perhaps not be seen, but disc Life Expectancy (LE) and playability

reduced is costly. Unless we are misreading it, the humidity barrier is

located at the reading side of the SACD, and such a layer is not located

under the lacquer to protect the reflective metallic layer from the label

side. The label and the lacquer could hardly be considered to have the

beneficial effect of the silicon-based compound applied by the CUBE UNO. But

that is an issue that should be investigated, i.e: From which side of the

SACD will degradation due to water absorption occur?

Philips/Sony further state: "DSD is a superlative solution for music

companies desperate to transfer archival recordings before they disintegrate

forever. The unprecedented frequency response and dynamic range means that

DSD will capture every nuance of the original, down to the noise floor and

below. The Hybrid configuration, that includes a two-layer approach, one

normal CD and an additional semi-transmissive high density (HD) layer,

enables a single disc to play compatibly on both standard CD and Super Audio

Compact Disc players."

That is why this latest optical disc design also includes Digital

Watermarking using visible and invisible approaches to offer a more secure

means of protecting the recordings against piracy.

The day when SACD writers will become available could be the time that audio

archivists have been waiting for, to gain protection for their audio

collections beyond the 30 year Life Expectancy barrier of regular CD media.

Yes, this implies that I do not accept the ridiculous and misleading claims

of life expectancy of 100 or 200 years, based on very short-term simulations

and very limited evaluation criteria that are not published, that are

misleading when applied to applications demanding long signal and content

life. I highly recommend the evaluation of the SACD systems that are now

available and thorough validation testing of the benefits of the humidity

barrier(s) included in SACD media.

Without measuring the state of a CD or DVD or SACD when new, to benchmark

its ability to not only record but also to maintain the signals, it is easy

for wishful thinking to influence the design of processes that the medium is

subjected to. Post-treatrment evaluation is a valid means to verify whether

such treatments cause immediate and short-term harm or degradation to the

signals. If measurable degradation is not evident in a reasonable number of

samples, then the method has been validated as a substrate reconditioning

method. Meanwhile we should not assume that we can expose optical disc media

that are vulnerable when exposed to water, high humidity and solvents. I

would also like to commend Jim Lindner of VidiPax in New York, NY., for his

offer to test 100 discs free of charge. I look forward to reading the

resultrs of the evaluations and commit to consider them as we develop

recommended practices for extended-term life expectancy of optical disc

media.

Best regards,

Ed H. Zwaneveld,

Technological Research and Development,

National Film Board of Canada, and

Chair AMIA Preservation Committee

August 24, 2000

I have also not mentioned many other issues being discussed such as effects of UV light on CD-R media - in a presentation given by Imation (a media manufacturer) at the AIC 2000 conference it was made clear that exposure to UV can have disasterous effects on CD-R media. Other issues include problems with varnish, inks, oxygen migration (disk rot), and of course obsolesence on a wide variety of levels. I encourage those interested in using CD-R media to follow some of this work - and for those less interested - my personal summary...... take manufacturers claims of this type with GREAT caution.

Jim Lindner
VidiPax - The Magnetic Media Restoration Company

Minister of Preservation and Access
VP General Manager VidiPax Division -
Loudeye Technologies
450 West 31 Street
New York, N.Y.  10001
212-563-1999 ext. 102

www.vidipax.com
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