Sorry to disagree with you Emeric...
The following is taken from a Media Science (a media testing facility) paper on CD-R technology:
Are green CD-R discs better than gold or blue ones?
This is an excellent question. Unfortunately, color is not a useful CD-R quality indicator. The human eye sees color in the visible portion of the light spectrum, while CD-R lasers operate in the infrared part of the spectrum. Only the interaction between the infrared laser and the organic polymer dye layer is important to quality, not visible color such as gold or green. Read lasers operate at a very low power level that does not alter the dye. Writers switch laser power to much higher levels that alter the dye during recording. The matrix of CD-R dye types, writers, firmware revisions, and recording software are far more complex than for CD-ROM discs.
CD-R discs first used a cyanine dye developed in Japan by Taiyo Yuden. Discs initially had longevity problems until stabilizers were added. Current products have good longevity. The blue color of this dye and the gold reflective layer combine to produce an emerald green or blue-green color. A relatively high laser recording power of 6.5 milliwatts is required at 1X, while greater intensities must be used at higher speeds. The relation between recording speed (1X, 2X, 4X, 6X) and power is non-linear. Although some uncertainty exists regarding the recording process, it seems that the laser bleaches the dye or alters its molecular structure in a manner that simulates pits and lands. A long write strategy is required, since the length of the altered region does not significantly exceed the region illuminated by the laser pulse. Taiyo Yuden licensed their dye to Ricoh and TDK. These companies also manufacture discs for resale under other brand names.
Phthalocyanine has excellent longevity and was developed in Japan by Mitsui Toatsu as an alternative to cyanine. The dye itself has little color and combines with the gold reflective layer to produce a gold-green or rich yellowish color. Laser recording powers are lower, about 5.5 milliwatts at 1X. Although greater powers are required at higher speeds, the relationship is non- linear. The recording laser may actually form depressions in the phthalocyanine dye polymer. These are significantly larger than the region illuminated by the laser pulse, requiring the use of a short write strategy during recording. Mitsui Toatsu licensed their dye to Eastman Kodak and to Mitsubishi/Verbatim. All three companies may manufacture discs for resale by other companies.
Recently the NCC subsidiary of Mitsubishi developed a metallized azo, or metal chelate, dye that is a dark blue color. Use of a silver reflective layer provides an attractive background for a label and combines with the dye to produce an unmistakable blue color when viewed from the readout surface. Azo CD-R discs are also marketed by Verbatim.
Taiyo Yuden established stabilized cyanine dye as a de facto reference for CD-R recorders. The appearance of Mitsui Toatsu phthalocyanine required recorder manufacturers to develop alternative recording powers and write strategies. These dyes utilize proprietary and patented formulas that may be modified from time to time. High speed, 2X, 4X and 6X recorders as well as azo dye has produced new challenges. This matrix of dye type and speed has produced constantly changing firmware revisions in CD-R recorders. Updates are generated as more is learned about the properties of the different dye types. Not all recorders use the same approach to recording power and write strategy. Therefore, certain writers may work best with certain media. Some manufacturers will supply the names of approved vendors upon request.
Reliance upon one type of dye, or even one brand, does not always produce high quality one-offs, since dye properties can change because of design modifications or lot to lot variations. Dyes are often applied by spin coating followed by a curing step, therefore properties can also vary from ID to OD. Also, third party dyes have appeared on the market. These are not Taiyo Yuden cyanine or Mitsui Toatsu phthalocyanine dyes, although visible colors may be similar. Their response to the infrared recording beam may be different from that of licensed dyes, resulting in different recorded quality.
Although awareness of quality issues is important, it is not necessary for the user to acquire expertise in dye chemistry, recording power, and write strategies. Instead, focus on regular testing that assures high quality one-offs. This requires specialized in-house equipment or use of an independent testing laboratory. Functionality in just one drive is not an adequate test, since verification using sector reads at the DOS level is insensitive to defects that cause the disc to fail in other drives. CD-ROM manufacturers regularly utilize sophisticated quality tests to assure interchangeability of their products. Anyone who generates one-offs must perform similar tests if costly or embarrassing field problems and product returns are to be minimized. Rely on test results, not color or brand name.
Bruce
