Help and How-Tos 

Not all CDRs are created equal

Editor's Note:  The aim of this article to help you understand why some brands of recordable CD's are not suitable for archiving and storing important computer files such as your photos or other important documents.  We hope that this article will arm you with the information you need to make an informed choice next time buy recordable CD's or DVDs.

Ron Kubara - FujiFilm - April 2004

Image permanence for CDR's (Compact Disk Recordable) is an area that is not well known or understood by the general consumer nor by many photo labs.  Contrary to popular belief, most CDR's are not permanent, reliable long term storage solutions.  Low priced CDR's can fail and become completely unreadable in as little as two years. A cheap CDR is great for moving files from one PC to another, but risky if being used to archive files or images. Quality CDR’s such as those from Fuji or Kodak utilize high quality recording and reflective layers and are well sealed to reduce the harmful effects of the human environment.

The material used for the plastic substrate (polycarbonate) of the CD & CDR is important, as it needs to be gas impermeable. Unfortunately no plastic is, but some plastics are better than others. Even more important is the quality and thickness of the top coatings used to seal layers coated on the substrate. The actual layer that holds the data is not sandwiched in the middle of the plastic CDR, but layered or coated on top, then sealed.

Prerecorded CD's are made by "stamping" the information into the plastic substrate then an aluminum alloy coating is applied to the "bumpy" stamped surface. The laser either reflects off of this reflective layer and a “1 bit” is determined, or the laser is deflected by the “stamped” bump and a “0” bit is determined. Contrary to popular belief, the recorded layer of a CD/CDR is not “sandwiched” within the plastic substrate. A clear lacquer protective layer is put on top of the aluminum reflective layer. A label is put on top or a thick ink coating applied. As the CD is read from the plastic side, a paper, plastic or ink label applied to the CD provides extra protection against the data surfaces from being scratched.

CDR's are not stamped with the data but burned later by the user. However the plastic polycarbonate is stamped with splines (tracks or lines) for the laser to follow. A recording layer referred to as the dye layer is sprayed on top of the splines. Four basic chemical formulas are used:

1. Cyanine / light green/blue in color (most common and lowest quality)
2. Phthalocyanine / transparent with a slight green tint (second most common)
3. Metallized Azo /blue
4. Formazan / light green

Note- CDR manufactures may modify one of these dyes and make a custom proprietary formula.

A reflective coating made of silver alloy; pure silver, or pure gold is layered on top of the recording layer. Although Silver will show the true color of the recording layer dye, gold will change the dye color because of its yellowish color. The burning laser melts a “pit” into the dye which then blocks the read laser from reflecting back, and a “0 bit” is determined. A good dye burns a nice clean pit so the read laser knows for sure if it is a 0 or 1 bit. If the burn is not clean and the edge is not a clean cut, the CDR will error.

To protect the coatings, lacquer is applied and high quality manufactures make it nice and thick or will even apply a separate protective coating. Poor CDR's have very little protection on the coatings and will scratch easily, or worse, delaminate. By writing with a non-water base felt pen, the ink could make its way to the data layer and damage a poorly sealed CDR. But be aware, even the best coated CDR’s can be damaged over time by non-water based felt markers.

It is difficult to use CDR color only as a guide, but as a general guideline, if the CDR does not have a color tint; it is likely a lower quality silver alloy with a poor dye layer. Blue, green and faint green CDR’s will be good if they used quality silver. Unfortunate there is no way to know for sure. Gold CDR’s are the best because when the manufacture uses gold, they use a quality dye. But don’t be fooled by manufactures that paint a gold color on the non-read side!

There are several reasons for good or poor CDR permanence;

1. Plastic (polycarbonate substrate) is oxygen permeable. Oxygen eventually makes its way through the non-lacquered side (as well as the lacquered side in some cases) and reaches the reflective. As Aluminum, Silver and Silver alloy corrode when exposed to oxygen, oxygen (air) reaching the reflective layers will corrode causing a read error. This could happen in as little as two years with poor CD's. Gold CDR’s are best in this area.
2. The dyes used in the recording layer are light sensitive and will fade over time. Quality CDR’s use a dye that resists fading. To be safe, store them in the dark.
3. Humidity may seep through a poor lacquer coating. Quality CDR’s are well sealed and resist seepage from markers and moisture. To make them last, store in low humidity and use water based markers and write on the center core.
4. A scratch on the base side can be repaired, but a scratch on the lacquer side makes the CD a coffee table coaster. Quality CDR’s have a thick protective coating to resist scratches.

Archiving reports vary by manufacture, but 70 years would be low for a quality CDR with the norm being 100 years. Some manufactures of Gold CDR’s claim 100-200 years!

You generally get what you paid for. Don’t put those precious images on a CDR that costs you just a few pennies!