[ARSCLIST] The ways CD's and DVD's can fail.

["Ronald W. Frazier" <arsclistinfo@xxxxxxxxxxxx>]

Hello all,

I am new to the list.  I am an independent consultant interested in 
exploring ways to archive data for long periods of time.  During my 
research, I compiled the following information which I thought the list 
members might appreciate.  Please excuse if this duplicates anything 
previously posted.

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  --  P.O. Box 2284  --  Cumming, GA  30028  --  770-205-9422 
(O)  --  404-431-5472 (C)
Email: rwfrazier AT macdatasecurity DOT com  (replace the AT and DOT by hand)
I am an independent consultant interested in exploring ways to archive data 
over long periods of time.
Recordable DVD's & CD's can fail in 2-5 years.  Don't let that happen to 
YOUR data.
   Get your GOLD Archival Grade DVD's & CD's from 
http://macdatasecurity.com/ today!
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