CD-R or CD-RW
Reply #17 – 2003-04-26 23:07:52
I experienced some (silver) discs turning yellow on the upper side over time, beginning at the outer diameter. You have to remember that cdr reflectors are mostly made of silver or gold ... not aluminium so I don't know if this can be called "CD Rot" in the sense of it's definition, although it surely is some kind of "rot", but not caused by acid or sulfur (my burned CD's that turned yellow were stored with AND without paper). Some people claim that insuffiecient sealing of the outer rim will allow oxygen to diffuse into the area between polycarbonate layer and reflector to oxydize the reflector itself and make the CD degrade and become unreadable as a final result. UV radiation can destroy the dye formation (and thus, the pit and land structures) ... enough destruction on the dye formation and the CD will be unreadable as well. Phtalocyanine (the "clear" dye) is believed to be the dye with the best UV resistance possible ... Azo or Cyanine (the deep or light blue/green discs) will suffer much more from UV radiation ... Some cheap media show a pit geometry totally out of specification (can be made visible via atomic force microscopy) ... the writing quality article (absolutely recommended) from www.cdrinfo.com explains this quite good ... this is a problem of the production process itself, some manufacturers sell the batches from production startup where production conditions mostly haven't stabilized (the prodcution chain will come to balance only after some hours of "warm-up") - other manufacturers (like Taiyo Yuden, I guess) will throw these batches away and only use/sell the batches that were produced on a perfecly running and balanced production chain ... Burner and Write Speed is another parameter that may influence CDR lifespan ... writing strategies (laser power, burst length) are stored within the burner's firmware and MUST match the appropriate media (which will be recognized by reading the ATIP) ... tests show that many burners do not adjust themselves as good as they could which explains different results with the same media type on different burners ... write speed is important as well ... too fast is never good, but burning too slow can lead to thermal problems (think about longer laser pulses over a longer time when writing at 2x or 4x where e.g. heat exchange from the disc to the surrounding air is lower due to lower rotation speeds) In theory, a pure gold reflector, in combination with phatlocyanine dye and good sealing (like e.g. Mitsui Gold Ultra or Hi-Space Gold), written at 8-16x CLV, would be the best choice for long-term data storage on CDR ... but these Mitsui or Kodak Gold discs are reported as slowly dying, too ... just my 2 cents ...