Nobody knows the longevity of CD-Rs. Even best assumptions include that the variation between various disc types is almost as big as the longest expected longevity time.
The only tests to _estimate_ the longevity are the accelerated aging tests (using temp/humidity delta) and then calculating results using Arrhenius formula. This is a basic chemical corrosion formula that can give you some linear extrapolation limits, assuming the initial test conditions were right (they aren't in most tests) and development of corrosion is linear on discs (it highly likely isn't).
So, Arrhenius formula based accelerating tests can be very misleading. However, they are the best we've got.
It is already know that disc longevity (i.e. data still readable 100% correctly with error correction using normal "within specifications" readers, not forensic tools) is affected by (but not necessarily limited to):
- radiation (particularly UVA/UVB)
- humidity (both relative and relative delta)
- temp (both absolute and delta)
- noxious gases (ozone, sulfour based gases, etc)
- solvents (both alcohol and grease based, even organic grease from human skin)
- disc dye chemical stability
- disc manufacturing quality (layer bonding, surface materials, UV filters, protective scratch layers, etc)
- initial burn quality (C1, C2, UNC and especially low level values such as ecc, jitter, wobble, HF, reflectivity, etc)
- handling (bending, labelling, writing, scratching, high speed reading, etc)
- organic growth attacking disc material (i.e. fungus)
So, there are way too many variables for anyone to test. So they have not been tested. Even the best of accelerated aging tests are almost ten years old now and done on disc/dye types that are not even manufactured anymore.
For practical purposes the longevity can be increased as follows:
- Choose only quality dye and quality disc maker (Taiyo Yuden would be my only choise, even Mitsubishi Chemical and Fuji Photofilm have had problems, imho).
- Choose only quality brands (from above makers!) that may cost more and contain additional disc qualities such as UV protective and scratch (label side) protective layers. Unscrupulous disc makers use identification codes or stampers from high quality makers, but still produce crap discs. Just reading the ATIP codes off the disc is no proof of a high quality disc (especially if you bought the disc in Asia or in Russia).
- store out from sunlight in a room temp in unchanging temp/humidity - away from noxious gas sources. Handle with clean hands. Don't use maximum read speeds (in case you get severely unsymmetric disc, it may shatter at 52x). Don't write anywhere on the discs. Don't use labels/stickers.
- measure error rates/readability (for crucial back ups) on a regular basis and make new copies of copies that start to detoriorate.
In short, it's not easy, nothing is guaranteed and anecdotal evidence like "my X year old Kodak is still working ok, all disc longevity fears are rubbish" is mostly useless, imho.
I've had Kodaks, Mitsuis, Ricoh, TDK (when they made some), Fuji Photofilm, Mitsubishi Chemical, TY, Ritek, MBI, MCC, Optodisc, etc fail on me.
I've had discs from all major manufacturers/brands fail in my 12 years of writing CD-R discs. Some just die on the dye layer, some peel of (starting from the label side), some become full of holes when looked against light (oxidization), some change colour unevenly and become unreadable, some just become unreadable with out any easily visible marks on them.
Then again I have stuff dating back as far as 1994 that I've still kept, which function not only well, but measure quite nicely as well.
So, it's possible for CD-R discs to stay readable for quite long time, but there are no simple/hard rules to achieve this (only the above heuristics).
What might give you some idea about cd-r longevity is that almost no storage professional worth his/her training uses cd-r as anything more than an interim storage media. It is not proven nor trusted for long term storage. Some discs will probably work for that, but as there is no good data to determine what kind of discs will, so professionals just can't risk it.
What's interesting that the industry is now starting to look at DVD+/-R disc longevity and quality, but many of the testing/estimation/quality control issues remain there as well.
The first useful accelerated aging test results for DVD+/-R discs from OSTA will probably be available towards the end of this year.
regards,
halcyon
PS Verbatim doesn't make their discs. They use discs made by TY, MCC and MBI (dependent on the disc type, i.e. DataLife, DataLifePlus, printable, crystal, etc.)