GoKawiilDiscussions about the thorny topic of computer data preservation are swirling again. This time, optical disc collectors are highlighting the danger of catastrophic failures of compact disc (CD) formats. Specifically, a handful of Twitter/X users have seen their treasured CDs split or shatter without any glaringly obvious cause. The root cause seems to be the degradation of the polycarbonate substrates of the CDs from either cleaning substances or some types of foam padding in storage cases off-gassing.
The two examples of shattered CDs embedded above might look pretty similar, but the failures may have been precipitated through different vectors. @japanretrogame’s split-down-the-middle CD was perhaps doomed due to too much care and maintenance. Reader notes suggest the user cleaned and polished this CD to keep it clean and shiny. This eventually caused chemical cracking of the polycarbonate substrate, it is thought [machine translations used].
Moving along to consider @CZ662C’s even worse-looking CD fragments, and the tech detectives on X reckon this dramatic damage was caused by storage in a foam-padded case. Some foam padding materials, the story goes, will off-gas ammonia compounds. Apparently sealed protective cases with (particularly polyurethane type) foam padding will off-gas, and if left sealed with CDs inside, the vapor can weaken, craze, or lead to cracking of the polycarbonate structure.
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Polycarbonate substrate damage is a greater danger for CD users as compact discs rely on a single layer of this plastic. DVDs employ two polycarbonate halves bonded together with adhesive, which makes them less susceptible to the above-outlined issues.
There’s also bit rot and/or laser rot to worry about
The dangers of bit rot and laser rot have caused far more significant blips on the optical disc user threat radar to date. Wikipedia classifies this kind of damage as being caused largely by oxidation of the reflective layer, reactions with contaminants, and ultraviolet light damage. DVDs can also suffer from de-bonding of the adhesive between the two slivers of polycarbonate in the disc.
Over the years, some brands of optical media have earned a poor reputation for longevity due to bit rot susceptibility. I’ve had numerous discs suffer this kind of damage. It is therefore important to back up optical discs, which may themselves have been backups at some point, to keep all your old digital treasures alive.
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