The standard for the longevity of optical discs is an area of overlap between a couple of ISO committees, however, the chair of one of the groups (from TC 42) used to tell this story.

A man is crawling around the sidewalk under a street lamp one night looking intently at the ground. Another person comes by and asks what he's doing. He replies, "I lost a valuable ring in that alley back there and I'm looking for it." The passerby asks, "If you lost in the alley back there, then why are you looking for it out here?" To which the searcher replies, "It's dark back there and I can't see a thing!"

This expressed the feeling of the ISO task group from TC 42 charged with drafting a standard for predicting the life expectancy of optical discs including CDs. 

They were very certain that the weak link was delamination and there was plenty of anecdotal evidence to support the idea, but no one had a test method for testing the potential for delamination. However, the standard is written around heat and humidity aging of the imaging dye. So it's a bit like basing the life expectancy of a car on how long the cup holders will keep a cup from tipping over while the car is in motion. 

So while manufacturers can claim that their CDs will last centuries based on a cited ISO standard, in reality, it doesn't mean very much because the first point of failure is most likely delamination of the disc.  

ISO TC 42 wasn't very satisfied with the outcome, but until someone can come-up with an appropriate test method, it's all that we have.

As Gordy points out, the manufacturers go wherever labor is cheapest to produce these discs and we knew that there wasn't much value to them when the manufacturers (of both tape and optical discs) all dropped out of the ISO "image" permanence standards. The last time that I bought writeable DVDs, from a major brand name, they were worth about 24 cents each retail. Cases for them cost more than the actual discs. So, of course these are a disposable commodity to the manufacturers.  At that price, they could hand out a lot of blank replacement discs before it significantly cut into their profits and how many people really complain about disc failure anyway. (Even if you did, there are so many things that the user could've done to cause the problem that it would be easy to argue against replacing the disc, although, again, for the cost of the disc, it's just not worth the effort to argue.)

ISO 18927:2013 IMAGING MATERIALS - RECORDABLE COMPACT DISC SYSTEMS - METHOD FOR ESTIMATING THE LIFE EXPECTANCY BASED ON THE EFFECTS OF TEMPERATUREAND RELATIVE HUMIDITY

Historically, there was a problem with the "silver" (actually aluminum)discs such that the reflective layer was corroding pretty quickly (converting the shiny aluminum to white aluminum oxide). The immediate problem was solved, but there has been a lingering distrust of the cheaper aluminum reflective layer.

After this problem was fixed, libraries were finding that CDs were lasting roughly four years before failure. 

-Doug
Douglas Nishimura
Image Permanence institute
Rochester institute of Technology


-----Original Message-----
From: Records Management Program [mailto:[log in to unmask]] On Behalf Of Gordy Hoke
Sent: Thursday, August 08, 2013 3:48 PM
To: [log in to unmask]
Subject: Re: Quality of CDs

Yes, there are large differences with potentially huge implications for records preservation.

Many, if not most, blank CDs and DVDs are made in SE Asia or Western China of unknown materials.  They are shipped (for China, first by rail to Shanghai/Hong Kong) across the Pacific to a West Coast Port, transported across the country, warehoused for delivery to a retail outlet, where they sit on the shelf for who-knows-how-long.

Budget-minded consumers buy a spindle of 100.  By the time they get to the bottom, how old are the organic dyes that record the data?  Nonetheless, they trust their precious family photos to these disks.  How likely is it that these pics will be readable by grandchildren, even if issues of hardware, OS, app software, file format, etc. can be overcome.  ...Oh, yes, and if the materials in the substrate don't deteriorate?

However, there are blank disks available that are dated at manufacture.  Some claim to be made according to ISO standards.  JVC claims 25 years viability for theirs in a controlled environment.

An LG peripheral I recently opened contained a flyer for a blank DVD that brazenly claimed to safely save data for 1000 years -- yes, a millenium!  I laughed.

The point is, there is a difference in disk quality and trustworthiness.  I suggest some research for the current state of affairs.  Caveat emptor.

As always, the capability of the medium should match the retention requirement for the record.


Best of luck,

Gordy
Gordon E.J. Hoke, CRM
[log in to unmask]
Waukegan, IL USA

-----Original Message-----
>From: Alice Young <[log in to unmask]>


Gordon E.J. Hoke, CRM

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