[Dixielandjazz] FW:How long do CD-Rs last?

[Bill Haesler]

Dear friends,
This one via the Australian Dance Bands list and its listmate Rudy Zeman.
A bit long and somewhat technical.
Kind regards,
Bill. 
               
            From the magazine of the Melbourne PC User Group
            How Long Will a CD-R Last?
            Gordon Woolf

      How good are CD-R discs? How long will they last? Will they be
readable in three months, three years, 30 years?

      When I read several reports of CD-R discs not being readable a few
months after they were written, I thought it time to find out more.
       
      It seemed scary: warnings from seemingly reputable sources. A lot
depends on how you treat the CDs and even more on the quality of your
initial recording, but there are discs around which are more likely to fail
than to work - one survey showed that six out of 10 discs can fail if you
select the wrong brands.
       
      As one CD duplication service states: "It is not advisable to leave a
CD-R upside down in bright light or the sun for a long time" but most failed
backups are not satisfactorily written in the first place. There are so many
things which can go wrong with a recording that manufacturers of poor
quality discs may get away with it for a long time.

      If you can write well to a good CD, it will probably last. But we've
probably all heard of companies happily backing up data to tape every night,
and never checking they can actually read anything back.
      Kodak say their accelerated aging tests indicate that their Infoguard
CD-R, which has an extra coating over the recording surface, will last 200
years. TDK say that their discs will last "about 100 years".
       
      Tests by West Deutsche Rundfunk in Germany support manufacturers'
claims of two or three years ago giving 10-20 years as the life of a CD.
Australia's National Film and Sound Archive also suggests a life expectancy
of 10-20 years compared to pressed CDs lasting around four times that long.

      John Spence, head of radio archives with the Australian Broadcasting
Corporation in Sydney, has been quoted, along with many others, as holding
the view that how long the CD-ROM format is going to last "is perhaps a more
important question".

            Figure 1. Dye layers on CDs and CD-Rs.
            Image from Web site
http://62.212.130.96/hardware/cdrom/cd_dye.shtml,
            a good reference for information on which specifications
            of CD-R are made by which companies.
           
            Jerome L. Hartke, of Media Sciences, Inc., has not tested
longevity but the more simple matter of writing and reading. He reports:
"The quality of CD-R discs from experienced manufacturers has improved from
30 per cent defective discs in 1998 to 13 per cent in 2000. Failures for
other discs increased from 33 per cent in 1998 to an alarming 60 per cent in
2000."
             
            In other words it seems that while the original manufacturers
are getting better, there are an alarming number of questionable discs
around. There's more information on this at
http://www.mscience.com/survey.html.
           
      The survey concluded: "Test results clearly indicated that all discs
were not alike, even if their colors were similar. Cost pressures have
resulted in a broad matrix of stampers, dyes, metallizations, and processes.
No correlation was observed between CD-R quality and dye type (cyanine or
phthalocyanine), metallization (gold or silver), or recording speed (2X-8X).
Quality is primarily determined by efforts at the manufacturing facility."

      Even so, many reports of extremely short life in discs could be due to
them being recorded on faulty or substandard equipment rather than of being
poor quality discs in the first place.
       
      The US standards institute has a committee (ANSI Committee IT-9) which
is working on guidelines for CD-ROM and CD-R life estimation. However, there
seem to be no standards for drives, other than an expectation that they will
work to the "Orange Book" specifications. So, the first question one has to
ask is whether one is getting a satisfactory disc in the first place, then
whether you are making a good recording.

      There are still many references on the Internet to a 1998 report in
'U.S. News and World Report' under the heading "Whoops, There Goes Another
CD-ROM" that quoted the life of data recorded on CDs as about five years.

            Figure 2. Woolly jumpers for your CD?
            They could certainly provide a different kind of protection but
they show an Australian adaptation of the woollen crochet CD coaster
referred to in PCUpdate, May 2001. They use a bad CD as stiffening to slop
up liquid spills before they damage the CDs you do want. The pattern is
available at: http://www.worsleypress.com/garagesale/CDcoaster.htm
           
            Laura Tangley wrote that unlike paper based landmarks of the
past, the essential records from today, including health and bank records
and research data, would quickly disintegrate.
             
            This has been denied by many in the industry. For example,
Stephen F. Nathans in EMedia Professional, wrote under the heading "Can CDs
Get Mad Cow Disease?" that while research by National Media Lab (NML) in the
USA using "accelerated aging" had stated that CD-Rs from "all major vendors
are acceptable for reliable data storage" for "at least five years", that
"the best vendors" of CD-ROM media can be expected to provide reliable data
storage for 50 years; CD-R's best and brightest clock in at 30 years, maybe
more.

            The reasons for differences in colour are explained in the
sidebar above. But even expert writers and researchers in this field refer
to a level of secrecy among the manufacturers which has only recently been
breaking down. 
            While some Web sites include tables of who produces what brand,
and what dye and metallic layer they are based on, there is no real way for
the consumer to know just where a minor brand CD-R was made and using what
dye. There are hints that even among the major manufacturers quality could
vary somewhat according to which factory the disc was made in.

      However, even if we stick to top brands, it is the standard of writing
the disc today which is going to have the greatest influence on how long it
will last. For example, this may be influenced more by the possibility that
the writing laser is gradually losing power or accuracy.
       
      Dana J. Parker, co-author of several technical books on CD-ROMs, is
quoted online as stating:
      "CD recordable technology is a complex and convoluted subject. There
are many factors that come into play when recording a disc: the rate of
spin, the formula of the dye, the ambient temperature, the internal
temperature, the age of the media, the power and wavelength of the laser,
the spacing and size of the marks on the media relative to the speed of the
disc, to name but a very few."
       
      At least you can discount the myth of "CD rot". It did have some truth
with early compact discs - which use aluminium as the backing, and where, if
the edge coating was incomplete, the aluminum could corrode through
oxidation (aluminium doesn't rust, but you will have seen that grey powdery
coating on older aluminium windows which is the equivalent).
       
      But there are some other problems. The silver coating used on some
CD-R discs may also be affected by sulphur, a common pollutant of the air we
breathe.

      Gold may be best, but cost means that gold layers tend to be very
thin, and so a thicker silver layer may be better than a thin gold layer.
Again, our descendants may know the answer. Ask again in 90 years.
      Early labelling inks managed to corrode the CD - and I'm sure I'm not
the only person to have written to a CD, checked that all is well, and then
grabbed the nearest marker to note the contents and by doing so created
another coaster.

      Water must also be avoided since polycarbonate will absorb water
molecules and oil from fingerprints or organic vapors in the environment can
also attack either surface. So where does this leave us? Somewhat confused.
And we have not covered John Spence's greater concern that it may be as hard
to find a CD player in 20 years time as it is now to find a Benoulli Box or
an 8-inch floppy drive. To keep the material you will also have to keep the
hardware.

      Those few of us who really need assured information retrieval should
be considering commercial services who use top quality discs, expensive
calibrated CD writers and clean rooms to ensure no dust or pollution
problems in the writing stage. I will continue to use the cheapest bulk-buy
discs for file transfers, and for progressive backups which I will dump in a
week or a month's time. But for true backups, I'll go for the more expensive
brands which at least make some reasonable claims at longevity.

                  Does Colour Matter?

                  Unlike an ordinary CD, the CD-R has an organic dye
recording layer between the polycarbonate substrate and the light reflective
layer. The polycarbonate is etched, or stamped, with a spiral groove,
usually called a "pre-groove", used to guide the laser beam. The laser beam
heats and melts the organic dye forming a series of marks which resemble the
pits of a pressed CD.
                   
                  The colour of a recordable CD can be misleading because
what you see is a combination of the colour of the dye, and of the metallic
coating which reflects through it. The gold CD-R uses clear phthalocyanine
dye and a gold reflection layer. The green CD-R uses cyanine, which is blue,
but with the gold reflective layer, it appears green. Recently the cyanine
formula has been altered to give a longer life and the gold reflection layer
has also been replaced by a silver reflection layer, which makes the color
appear blue. 
                 
                  Other blue media are made of azo pigments. The colour may
seem similar to the more recent cyanine/silver combination but manufacturers
claim these blue discs are as durable as golden ones.

                  Colour does not matter to the recorder. In the light range
in which they work, all the colours will appear the same.

                  Phthalocyanine is less sensitive to ordinary light than
cyanine but has a narrower range for writing with laser light. Most CD-R
drives are based on using the original Taiyo Yuden cyanine system licenced
by Taiyo Yuden to TDK and Ricoh, who in turn make discs for many other
companies.

                  Phthalocyanine was developed by Mitsui Toatsu as an
alternative to cyanine and licensed to Eastman Kodak and to
Mitsubishi/Verbatim. All three companies may manufacture discs for resale by
other companies.

                  Mitsubishi developed the metallised azo dye that, used
with a silver reflective layer, provides an unmistakable blue color. Azo
CD-R discs are also marketed by Verbatim.

                  More recently, third party dyes have appeared. These are
not Taiyo Yuden cyanine or Mitsui Toatsu phthalocyanine dyes, although the
colours may be similar.
           
 *Reprinted from the June 2001 issue of PC Update, the magazine of Melbourne
PC User Group, Australia