Chip's CD Media Resource Center:
The most commonly asked questions about blank CD-Rs are probably "What kind is the best?" and "What kind should I buy?". Sometimes I think there is more info on the web in response to these questions than all other CD information put together. Regrettably, there is not really a simple answer, especially since the question is a moving target.
Comparisons of blank CD-Rs made in the past few years have revealed considerable differences in quality and longevity. So it really does matter what kind you choose. It may be that all brands are getting better as the industry matures and that the most egregious failures are behind us. But then again it may not.
A careful answer to question of what kind to buy would have to begin with the counter-questions, "What do you want to do with it and how long must it last?" But I'm not always a careful person, so for the benefit of the impatient, I'll say up front that from everything I've read, the premium CD-Rs from Kodak seem to be mentioned most often as "the best" according to criteria of low error rate, durability and longevity. No doubt there are many other opinions.
So now lets look at the qualities that differentiate CD-Rs.
There are four major physical factors that differentiate CD-Rs.
And a fifth factor that cannot as readily be discerned: the quality and care with which the disc is manufactured and shipped. The best materials in the world won't make a decent disc if the stamper (used to create the pre-groove) is worn out, the metal layer is unevenly applied, the dye has contaminants, or the discs were exposed to high heat, light or humidity before you got them.
The important thing here is how much light (at the laser wavelength) the metal reflects. Stamped audio CDs and CD-ROMs use aluminum which is inexpensive and provides adequate reflectance. CD-Rs, however, require a "shinier" background. That's because the dye layer attenuates the beam before it reaches the metal "land" areas, then attenuates it the reflected light again as it bounces back to the pickup. A highly-reflective metal layer helps compensate for this light loss.
Metals commonly used in CD-Rs are gold and silver. Silver is more reflective than gold, but silver is more subject to being corroded by the dye and (over time) other environmental factors. On the other hand, silver is much less expensive and there are ways of addressing the corrosion issue.
As you can imagine, manufacturers can save a lot of money by using as little silver or gold as possible. So there is a natural desire to make the metal layer very, very, very thin. There's an old saying that "You can't be too thin or too rich." Well, there is such a thing as "too thin" when it comes to metal layers (and it's a stupid "old saying" anyway). If the metal layer is too thin it becomes translucent and thus less reflective. A too-thin gold layer is worse than a silver layer of adequate thickness. If the metal is too thin, the reflectance is likely to vary over the surface of the disc, which can cause problems for both reading and writing.
The dye used in the original CD-Rs was called cyanine, developed by Taiyo Yuden, a Japanese company. They patented the dye, which meant that aspiring competitors had to invent their own dyes. This led to pthalocyanine, azo and Formazan.
Each dye type has its own distinctive color, but since the dye is translucent, its actual appearance on the disc depends on the color of the metal layer behind it. Thus cyanine, which itself is blue, appears green on a gold disc, while on a silver disc cyanine looks blue or greenish blue. The table below lists the common dyes used today in CD-Rs, with their patent holders and colors. Data is from CD Media World.
Some terms that you may hear:
The dye type is encoded in the pregroove of CD-R blanks as a small integer; a standard code number is assigned for each type. The list below is from CD Media World and summarizes the standard dye types, and the manufacturers that use them. You will sometimes encounter people talking about the properties of "Type 1", "Type 5" or "Type whatever" dyes, so this list may be helpful.
Note: At this time I'm not certain whether the list of manufacturers just denotes actual disc manufacturers that license the the dye, or whether it also includes vendor brand names under which these discs are sold. More work to be added here...
Unfortunately, the dye type encoded in the pregroove is not always correct. The reasons for this are explained in the next section, "Identifying the Manufacturer and Dye Type of a CD-R".
We've previously seen how the pregroove of a CD-R contains extra information, including ATIP and codes that identify the manufacturer of the disc, type of dye used, starting power level, etc. There are various tools, such as CD Identifier which will read this region and report the results. Sounds great!
Unfortunately, it appears that this data can be completely bogus. The CD-Recordable FAQ, item 2-33, includes this quote from Charles Palmer of cd-recordable.com
"Two components that many users of these programs always take as gospel are Media Manufacturer and Dye Data. These two readings are next to worthless.
The reason for this is that many CD-R manufacturers (like CD- Recordable.com) purchase their stampers (the nickel die that all CD-R substrates are molded from) from 3rd party sources. These 3rd party sources (either other disc manufacturers, or mastering houses) encode the data that these 'Identification' programs read, at the time that the original glass master is encoded. The 'Manufacturer' information that is encoded is usually the name of the company that made the master. Since stampers made from that master will be sold to disc manufacturers the world over, all of discs that those manufacturers produce from those stampers will contain the same 'Manufacturer' information. Information which is obviously quite erroneous and irrelevant. Very seldom will the 'manufacturer' information encoded on a CD-R actually tell you anything other than who made the original master. [...]
The second piece of data (the dye type) is also dubious. Because most master/stamper configurations are designed to be matched to specific dye types (Phthalocyanine, Cyanine, Azo, Etc), the 'Dye' information that is encoded when the master is produced indicates the type of dye that the master was designed for. This of course, does not assure that the manufacturer that buys and uses this stamper will be using it with the dye that it has been designed for. It is quite possible that a stamper/dye combination is used by a CD-R manufacturer that contradicts the 'dye' information encoded on the master. Therefore that information becomes as potentially misleading as the 'Manufacturer' data discussed earlier."
Experts are entitled to opinions. Marketing folks are paid to have opinions. With respect to CDs, I am neither. I am, however, attempting to accurately research and assess the available information. Therefore, included below are some opinions found on the web. As to whether a given opinion is from an expert or a marketeer, you will have to be the judge.
The following section is from EMTEC:
When CD-Rs were first introduced, disks coated with phtalocyanine dye (gold) had better stability and recording characteristics. However, cyanine dye technology has progressed significantly. The archival stability of cyanine dye has been greatly improved and cyanine dye-coated CD-Rs (greenish-blue & blue-silver) can now be recorded at 1X to 8X writing speeds. These enhancements have made cyanine dye disks the best price/value alternative and the current market choice.
On the other hand, Octave Systems says...
Pthalocyanine dye is superior to the Cyanine dye used in other CD-R products for two reasons. One, Pthalocyanine dye is far more stabile than Cyanine. The information recorded on a Mitsui CD-R will last for over 100 years. Cyanine based products might last 20 years. Secondly, Pthalocyanine dye is optimized for use in higher speed writers such as 4X and 6X.
This success is due to the accuracy with which laser light is able to create "pits" in the Pthalocyanine surface. Pits etched into Cyanine-based disks at high speed can be shallow or poorly defined, resulting in a poorly written disk.
Pthalocyanine has outperformed Cyanine in a series of tests when subjected to light, heat, and dampness. These test results below highlight the difference.
More opinions to come...
Last Updated Monday October 15, 2001 17:58:27 PDT