This was a reply to someone else over in the archives list. I thought you
all might appreciate the information as well.
----------------------
I thought CD's and DVD's were nearly indestructible until I read the
website I linked to earlier. After I started checking into it, I found a
number of pieces of evidence that the data on recordable discs can indeed
self destruct over a short period of time. My research is still a bit
incomplete, but I'll share a few things I've learned.
A commercial DVD of a movie, as I understand it, is PRESSED from a glass
master disc. Thus, the reflective surface of the disc actually has little
pits in it which the laser beam reads. This type of disc can last a very
long time.
A recordable disc does not have any real pits. The reflective surface of
the disc is coated with a dye which either evaporates and changes color or
creates a bubble when the laser beam writes to it. This type of disc may
not last nearly as long for the reasons below.
I have talked to a rep at the factory that makes archival grade discs. He
explained several ways that a recordable DVD (or CD) disc can fail.
A recordable DVD is made by sandwiching a dye coated reflective layer
between two plastic layers, along with various coatings and glues.
Failure mode # 1: OXIDATION - I found out that the plastic part of the
disc is not waterproof, despite what we might think. Water vapor can seep
through the plastic over time. Once that happens, it can cause oxidation
of the reflective surface. If the reflective surface is made of a material
that can oxidize, it can become unreadable. Aluminum can corrode. Silver
can tarnish. The best way to prevent oxidation is to use a material that
cannot oxidize. The best material for that is PURE GOLD. So, an archival
grade disc should have pure gold at its core. Not just a gold color, real
gold.
Failure mode # 2: DYE FAILURE - The chemical dyes used in recordable DVD's
intrinsically go through chemical reactions over time that change their
color and reaction to the laser beam. Certain dyes have been proven to
have a shorter life span and others a longer life span. The worse ones can
change in just a few years to the point that the disc is unreadable. How
do you know which is which? The only way is to look at documented
accelerated aging tests on the media. If you want a buzzword to look for,
go for Phthalocyanine (tha-lo-sy-a-neen). According to my research, this
is the best available. However, I believe this applies only to CD's. I am
looking into the DVD aspect of things. Make sure the vendor is really
using this dye, and not just putting it on the marketing materials. An
archival grade disc should use premium long life dye.
Failure mode # 3: BONDING FAILURE - As mentioned above, the DVD is
produced by bonding two plastic discs together with the reflective surface,
the dye, coatings, etc. Some manufacturers don't use as high quality
bonding agents as others. Also, the 'glue' doesn't always extend fully to
the edge of the plastic discs. So, if the disc has bonding problems, and
you drop it on its edge, it might delaminate. This could cause it to
become unreadable. An archival grade disc should use premium bonding
agents and edge to edge coverage.
Failure mode # 4: SCRATCHES - If you've used recordable DVD media very
much, you probably know they're extremely susceptible to scratches. Put
enough scratches on the disc, and it will become unreadable. And, it
doesn't take too many to make that happen. The way to prevent this is by
careful handling and with a scratch resistant coating. An archival grade
disc should have a scratch resistant coating.
Failure mode # 5: PRODUCTION QUALITY - I was told that many name brand
disc sellers bid the production out to the lowest bidder. There aren't
many DVD and CD factories in the world. But, an archive grade disc is not
likely to come from the lowest bidder. Also, some of these brands change
factories from time to time as they get new bids. Therefore, the quality
may vary from batch to batch. An archive grade disc should come from the
same factory all the time which should maintain world class quality
control. Note, I didn't say the owner of the brand had to manufacture the
discs. But it is essential that they get their discs from a world class
factory.
Well, that's about it for now. I hope everyone finds this information useful.
Sincerely,
Ron Frazier
------------------------------
Ron Frazier - owner of http://groups.yahoo.com/group/futureenergynow/ ,
http://groups.yahoo.com/group/futureenergyproducts/
http://c3energy.com/ --- http://c3energy.com/alt_energy/
http://c3energy.com/computersecurity/ --- http://c3energy.com/health/
I am an independent researcher / consultant specializing in Alternative
Energy and Data Security.
I am particularly interested in exploring ways to archive data over long
periods of time.
Ron Frazier
4050 Dorothy Dr.
Cumming, GA 30041
770-205-9422 (O) 404-431-5472 (C)
Email: rwfrazier AT c3energy DOT com (replace the AT and DOT by hand)
List archives at http://lists.ufl.edu/archives/recmgmt-l.html
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