Re: [ARSCLIST] CD-R dyes for archival uses

[Dave Radlauer <Dradjazz@xxxxxxx>]

In a message dated 1/20/04 9:01:18 PM, LISTSERV@xxxxxxx writes:

<< However, after a few years some CDRs are showing increasing error
rates, and some tracks become unreadable. >>

Since the topic of CD-R has been raised again, I offer the following taken 
from various websites:

Dave Radlauer

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First, it is actually amazingly difficult to get reliable and coherent
information on this so we understand why there is so much confusion and
misinformation around. Here's the deal:

The basic building blocks of CD-R media are cyanine dye, which is cyan blue
in color, and phthalocyanine dye, which is more or less colorless. The
reflective layer is either a silvery alloy, the exact composition of which
is proprietary, or 24K gold. There are gold/gold, green/gold, silver/blue,
and silver/silver CD-Rs. The apparent color is determined by the color of
the reflective layer (gold or silver) and the color of the dye (cyan or
colorless). For example, green/gold discs combine a gold reflective layer
with a cyan-colored dye, resulting in a gold appearance on the label side
and a green appearance on the writing side. The reason why there are
multiple formulations is that the materials and process for each are
patented. If a new vendor wants to get into the CD-R market, they have to
come up with a new combination of materials that conforms to the Orange Book
specifications.

Discs using the cyanine dye tend to have a wider tolerance for varying laser
intensities, but the theory is that discs made with phthalocyanine dye will
last longer. Of course CDR longevity is a hotly debated subject itself with
few agreed upon facts. Discs using silver reflective layers are reported to
have better reflectivity (gain) than gold discs, as well as better heat
transfer when burning, but gold reflective layer discs are supposed to last
longer. The gold discs also cost more to manufacture.

Which is best? There is no answer to this question. Besides these basic
building blocks there are a number of other variables in CDR manufacturing.
The thickness of the dye or reflective layer can differ. The groove
structure of the disc can be optimized for certain kinds of writing speeds
and so forth. There are many, many variables. The bottom line is that all
media today is light years better than it was just a few years ago (when
they were $30 a disc). BLER's (Block Error Rates) have gone WAY down. Also,
all discs have always had to conform to very rigid Orange Book standards.
Players and recorders, on the other hand, have not. And that's where the
trouble lies. They can vary wildly in their ability to read and write to
various media. So, at the end of the day the only thing that ultimately
matters in CDR media selection is what works with YOUR CD burner and CD
players. There is little rhyme or reason to this. Some discs work great in
one player, yet cannot be recognized or may skip wildly in another.
Fortunately most burners you buy will recommend a specific type or brand of
disc. We recommend you follow their recommendations. Beyond that anything
you learn will be mostly by trial and error. Do not get caught up in the
common sense that one type is inherently better than the other. We say the
differences aren't that significant. The only thing that matters is what
works well in your machine.

*****************************************************

Preventing CD-R Errors: Step 2, The Recording Environment 
CD-R media, like any other recording media, and CD-R drives, like any other 
storage devices, are susceptible to environmental factors. A cold, hot, dusty, 
wet, or humid room can have an adverse effect on the ability of your hardware 
to record an error-free CD. Likewise, media must be treated like any other 
storage medium. Check the manufacturer's recommended operating conditions for 
both your media and your recorder. Recorders generally will operate well at 5 to 
40 degrees Celsius and 25 to 80% humidity, with no condensation. Make sure 
your power is not subject to brownouts and check that the surface upon which the 
recorder is placed is not subject to vibration. Any vibration over .5G can 
cause the recorder to produce errors that are difficult to track down. A recorder 
sitting on top of an air conditioner, for instance, will suffer from 
excessive vibration; there have been reports of seemingly untraceable errors on discs 
that were recorded in facilities that are in or near the flight path of 
jetliners. 

Treat your media as you would any other recording media. If you store your 
media in a cold basement, give it a chance to acclimate to the prevalent 
conditions in the room where your recorder is located before you record to it. The 
best policy is to make sure that your media is stored in the same room where 
your recorder operates. When you receive your latest batch of media from Federal 
Express on a winter morning, give it a chance to warm up before you pop it 
into the recorder. Likewise, don't power on your recorder and immediately insert 
and record a disc. Give the recorder a chance to warm up, too. The best 
practice is to insert your blank media into the recorder while you are assembling or 
writing your image. During this period, the media and recorder will equalize 
in temperature. 

Preventing CD-R Errors: Step 3, Media and Recorder and CD-ROM Drive 
CD-R media, like any other recording media, is available from various 
manufacturers and distributors. Unlike other recording media, it has more 
incompatibilities with different recording devices. A 9-track tape, 3480 cartridge, 8mm 
tape, DAT, or 2120 tape is likely to work as well in one tape drive as another. 
Not so with CD-R media. Although the reasons that media works well in one 
drive and not in another have yet to be fully investigated and documented, the 
fact is that you will find that one or two particular brands of media will 
record with more reliability than others in your particular drive. 

Media costs do vary and, like everything else, many times this is an 
indication of quality. Like everything else, it also may be no indication of quality 
at all or there may be a price/quality tradeoff that may or may not hold true, 
depending on recording equipment. The best strategy at the outset for minimal 
error recording is to use media made, labeled, distributed or recommended by 
the manufacturer of your drive. If you are successful there, you may then begin 
to experiment with other media and you will soon find what works well and 
what doesn't. 

Those who use CD-Recordable with any kind of regularity soon learn through 
trial and error which brand of media performs best on their recorders for their 
particular applications. The infrequent or new user may never get to this 
level of expertise, however; and such users may end up so disillusioned that they 
reject CD-R technology altogether. Even the CD-R user who sticks to one 
supplier or one brand of media may face these problems, since there is always the 
possibility that he or she will receive a bad batch of media, or that the 
supplier may substitute another make of media for the one that works so well. 

Still, it's not that complicated. There are only two basic types of media: 
cyanine and phthalocyanine, and there are fewer than a dozen manufacturers of 
all CD-R media worldwide. Suppliers and vendors are numerous, however, and may 
offer one manufacturer's media printed with the vendor's label this week, and 
another brand identically printed the next. The only ways to avoid this 
contretemps are to use the media recommended by the manufacturer of your CD-R drive, 
and to learn to recognize media by its manufacturer's mark, rather than by the 
vendor's label. 

Nor are all CD-Recordable drives created equal. As a general rule, you can 
expect to get what you pay for, although recent pricing breakthroughs have 
resulted in some lower-quality drives being priced higher than their higher-quality 
newer competitors. There's more to buying a drive than the hardware and 
features of the drive itself, however; and customer support, caliber of 
documentation, and supporting software should be of equal consideration. Even more 
important than the quality of the recorder is the stability and suitability of the 
host platform because nearly every recorder will perform as expected in the 
right environment. 

Perhaps the most important consideration in determining whether a CD-R disc 
is viable or not is the CD-ROM drive that will eventually be used to read the 
disc. For example, the MIS department that creates CD-R discs that will be used 
within the company can reasonably expect that their discs are good enough if 
they can perform a byte-for-byte comparison against the source image on every 
disc, using a similar CD-ROM drive. This does not ensure that the discs are 
free of E32 errors, but it does give some assurance that the discs will be 
readable on their company's internal CD-ROM drives. 

A CD-R service bureau that creates discs for their clients in a production 
environment may face a different situation, however. They may have no way of 
knowing on what type or class of CD-ROM drive their CD-R discs will be expected 
to perform. Because CD-ROM drives differ not only in the efficiency of their 
error correction, but also in the ways that the differences in efficiency 
manifest themselves, it may not be enough to perform a byte-for-byte comparison on 
drives that represent the worst-case scenario. One drive's readable disc may be 
another drive's coaster. The service bureau might be well-advised to 
spot-check every disc produced on a dedicated CD testing system to ensure that all 
parameters are within specifications. 

The company or individual that uses CD-R as input for mass replicated discs 
presents yet another testing milieu: discs may be produced daily or weekly for 
testing or development, but only once in several months, perhaps, will a disc 
be created to be used as input for mass replication. The development discs, 
because they are for internal use, may not ever require testing, but the disc 
that is to be used as a master for a replication run of hundreds or thousands of 
discs should be of the very highest quality possible, and tight production 
schedules may even necessitate the creation of two perfect masters. This ensures 
that there will be no delays at the manufacturer's due to an unreadable or 
error-prone master disc. Once the discs have been mass-produced, the disc 
developer may find it wise to use a bit-for-bit comparison to ensure that what was 
recorded on CD-R was faithfully reproduced in pressed CD-ROM. 

OVERVIEW OF CD-R DYES

There are currently three competing organic dye polymers that are used to 
manufacture recordable CD's (CD-R). To date there has been no conclusive proof 
that any of these dye polymers are superior. Manufacturers (and some customers), 
however, have preferences based on a variety of factors including 
perceptions, personal (or secondhand) experience, and cost.

CYANINE (including METAL-STABILIZED CYANINE)

This is the original dye polymer used in the Orange Book specification for 
recordable media. Discs using this type of dye can be identified by the emerald 
green or cobalt blue. (The dye itself is blue, but will appear different based 
on the material used for the reflective layer. A gold reflective layer will 
produce the green while a silver reflective layer will produce the blue).

When the recording laser heats the dye the chemical composition is altered 
and the dye will allow less light to pass through, effectively simulating a 
"pit" on a replicated CD.

Many involved in this industry believe that Cyanine discs are better suited 
for a wider range of recording speeds and writing techniques. In particular, 
TDK claims that it's metal-stabilized cyanine discs were formulated to produce 
better quality with a wider range of CD-R burners (TDK can handle 6.5 mW +/- 
1.0 mW while phthalocyanine can only handle 5.5 mW +/- 0.5 mW) The argument 
against cyanine dyes is in it's native state cyanine is extremely sensitive to 
light and that there is the possibility that data could be lost after long 
exposures to light. This is not to say that data will be lost overnight; the 
proponents of the other dye types instead claim that the cyanine dye will hold data 
for only 20 years (70 for metal stabilized), while other types will last longer.


PHTHALOCYANINE (pronounced thal-o-sy-a-nene)

This dye (almost a clear yellow-green) produces discs that appear gold or 
greenish gold. We presume that this is based on a gold reflective layer and that 
a silver reflective layer would produce a silver or greenish-yellowish silver 
disc.

When the recording laser heats the phthalocyanine dye it causes it to melt. 
As it melts the polycarbonate layer below the dye expands to fill the gap. This 
melted "blob" effectively diffuses the light enough to resemble the pits on a 
replicated CD.

The estimated life of phthalocyanine discs is pegged at 100 years.

AZO

This formulation was developed by Mitsubishi and is offered in the US by 
Verbatim. It is easily recognized by it's deep blue color, partially caused by 
it's unique silver alloy reflective layer.

There is not an abundant source of information on this disc, which is 
surprising considering that it is a price leader and is currently one of the products 
most requested by our customers. The manufacturer claims that it has a data 
life of 100 years.

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