Originally posted by BoSkin
I. Components of a CDR
The polycarbonate disc is the basic component of a CD-R.
It has a very important role as the reader will notice when reading the section about the manufacturing process (molding).
The polycarbonate disc is covered by an organic dye where the information is stored.
The dye will decompose under the effects of the heat generated by a laser beam (wavelength of 780-790 nanometers).
The dye blackens under this effect and the information is created.
Gold or silver
A gold reflective layer is applied under a vacuum. The layer reflects the laser beam which reads the CD.
For economic reasons, silver has gradually replaced gold so as to reduce the cost of the end product as well as increase the reflectivity.
Nevertheless, CD-Rs with silver rather than gold layers have a shorter lifespan.
A layer of lacquer is applied to cover the gold completely. It goes beyond the edges and center of the disc in order to prevent any peeling (as the layer of gold tends to peel easily and humidity might therefore infiltrate).
This layer is baked under ultra-violet light for two seconds.
A resistant protective layer is applied to the lacquer which makes the medium impervious to scratches.
This is the final stage before the packaging.
It consists of printing graphic information onto the CD-R, such as manufacturer's name, type of product, etc...
II. Data layer
In CD-R, the organic dye sandwiched between the polycarbonate substrate and the metalized reflective layer of the media.
CD-Recordable discs do not have any data on them until they are recorded.
Instead the recording laser selectively melts "pits" into the dye layer -- but rather than burning holes in the dye, it simply melts it slightly, causing it to become non-translucent so the reading laser beam is refracted rather than reflected back to the reader's sensors.
In pressed CDs, the data layer is part of the polycarbonate substrate, and is pressed into the top side of it by a "stamper" during the injection moulding process.
Blue dye ( recording layer ) on gold ( reflective layer ) looks green, on silver - blue.
III. Dye characteristics/Longevity
In general, Cyanine dye is the de facto standard;
the Orange Book was written based on the original cyanine dye discs from Taiyo Yuden.
Most CD-Recorders are optimized for cyanine dye.
Cyanine discs are compatible with a wider range of laser powers.
Phthalocyanine dye has performed better than cyanine dye in accelerated age testing,
and may work better in higher speed recording (which requires higher laser powers.)
However, all of these differences aside, it appears that IN MOST CASES,
the two types of discs perform in essentially the same ways -
it's at the extremes and in the worst-case scenarios where these differences appear most marked.
There are many factors besides the dye composition that determine the quality of a CD-R disc.
Each media manufacturer strives to balance the engineering characteristics of the dye to insure greater compatibility with recorders and readers and long archive life.
Cyanine dye and its metal-stabilized derivatives were originally used because the Orange Book Part l referred to the recording characteristics of cyanine-based dyes in establishing CD-Recordable standards .
So, dyes based on cyanine tend to have a wide range of acceptable recording power levels and recording speeds .
The phthalocyanine dye is a newer dye that appears to be less sensitive to exposure to light after recording so that longevity has been improved.
Azo dye has been used in other optical recording media and is now being used in CD-R. The media manufacturers use these different dyes in combination with dye thickness, reflectivity thickness and material and groove structure to fine tune their recording characteristics for a wide range of recording speeds, recording power and media longevity.
Lifetime estimation of any storage medium is a very complex and statistical based process.
The CD-R media manufacturers have performed extensive media longevity studies within these industry defined tests and mathematical modeling techniques with results
claiming longevity from 70 years to over 200 years .
The primary caveat is how you handle and store the media. With proper handling and storage, your CD-Rs will outlive you.