Here we are discussing the shelf life of recordable (burned) CDs and DVDs that we all make at home using our burners. Not to be mistaken for commercially manufactured music or software CDs, or movie DVDs that you buy off the store shelves. There is a big difference between the two.

Commercially manufactured CDs/DVDs stamp their data on the disk. Commercially "stamped" CDs and DVDs have the data recorded by actually burning tiny pits in the substrate and also have a special clear protective layer on both sides to ensure their longevity. In general, these will last for a very long time - some manufacturers claim 100 years plus! You are more likely to lose these by breaking or scratching them than by losing the data on them.

Home burned disks don't do this, they record the data in the dye layer on the writable disk and the biggest danger to this is exposure to strong sunlight.

The best information available for Burned Cds and DVDs (and it's definitely somewhat limited since CD-R has only existed now for 14 years or so) is that QUALITY disks burned on a quality PROPERLY WORKING drive, will last at least 50 years and some estimates go out to 300 years (it goes without saying that no one has been able to test even 50 years in real world conditions).

First rule of thumb: nothing lasts forever. I don't care how well the recordable CD/DVD media is made, what colour or material it is made from, one day it will eventually fail. Second rule: if you highly value your important data, you shouldn't rely solely on your burned CD/DVD media to be your backup. You should have multiple backups in addition to your media, like a backup hard drive or flash drive.


RWs
A word about CD/RWs and DVD/RWs. These are much less reliable than CD/Rs and DVD/Rs. They use a magneto/optical technique for recording and erasing the data and this has a much shorter shelf life. Think of it as the difference between writing on a sheet of paper in ink and storing it away (R) and writing in pencil, erasing, writing over, erasing again, etc., (RW) the write-erase-write cycle will wear the paper out very quickly.


Quality:
So, assuming you are backing up to CD/R or DVD/R, what can you do to ensure maximum shelf life? First, buy a good quality disk, it really does make a difference, the "bargain basket" type disks will fail much quicker. There have been many debates as to which is the best dye colour for longer life. Personally, I can’t really say I've seen a difference, though I don't get as good results with the silver disks that are almost translucent. I tend to buy purple or gold colour disks but I'd have a hard time justifying that!

OK, so you've recorded the disk, what do you do now? DON'T write on the disk, even with one of the pens supposedly safe for the job and DON'T stick a label on the disk. Either buy the full face printable disks and put them in a suitable inkjet printer or use one of the special pens to write a code number in the transparent circular area near the hub and print the actual data on the case label.

For long term storage, put the disks in individual cases, preferably the ones with a black backing on the recoding surface side. Don't store them in the cd carriers. Keep the disks and cases in the dark. Strong sunlight, temperature and humidity can of course affect the life span. Store discs vertically if possible.

CDs can lose their reflective coating in other ways too - oxydation, scratches, even melting in a hot car. A DVD on the other hand has an extra layer of plastic atop the reflective section thus is less prone to problems of this type. They are not without their own issues though. Many DVDs have proven to be prone to a problem called "delamination" which is oddly similar to the older "bronzing" problem of CDs

DVDs should not be flexed (including when removing them from a case), scratches can do obvious damage, etc. etc.

Of course, I'm assuming you are already careful with handling the disks, hold by the edge only, don't get finger marks on the recording surface and don't step on them and keep them dust free.

If what you are storing is really important, then you might want to make two copies and then check one of them and even burn a new one every few years or so.


DVD RW Drives:
There are good drives, there are bad drives and there are good drives that have become defective. It is my personal opinion that a lot of the problems that we have are caused by drives whose laser output power levels are below spec. That can happen even to a high quality drive that was once good (it can also happen simply because the optics have become dirty). So the media isn't heated to the proper temperature, the dye doesn't fully change its reflectivity and you get a burn that consequently has poor long term stability.

I've had the best luck with Samsung (now TSST) and Pioneer and, frankly, much worse luck with almost all other drive brands
I have a mantra that I repeat to all my customers - "there are two sorts of people - those who have lost data, and those who will".

This leads to my rule number 1 - do not use the latest and least interchangeable technology for long term use, so I personally would not use DL DVDs. (double layer).

This is my rule number 2 - for anything that is precious, use high quality media.

This leads to my rule number 3 - always have two copies. However, don't make these two copies on identical media from the same batch. Use different ones. For example, with digital photos, every few weeks that you have taken them, as well as storing them on your hard disk, write them out to a CD. Then when you have about 6 CDs, put them onto a DVD, so that you now have two copies on different media.

"Laser Rot" What is Laser Rot? Laser Rot is a condition at which the mylar backing of the CD or DVD eventually wears out or looks like it develops spotting from severe and excessive reading. The mylar backing is the surface at which the laser light that is emitted is reflected off of and refracted by the pits in the plastic surface that makes the disc "readable." This use to be a very common issue with recordable optical media, but, has long become nowhere near as much of a severe issue these days.

One thing to keep in mind is the quality of the media and the mylar backing. Never ever use discs that are just the backing on a plastic disc, for this can be very easily damaged and is more prone to rotting out. Most discs now consist of the clear plastic discs at which the pits are burned into, the mylar reflective surface, and a translucent or colored cover/label surface. This three layer process makes the discs a little tougher and less prone to damage and keeps rotting down to a minimal.

Now, even without reading, if you are not using good quality discs, the mylar surface can also self-distruct, just start decomposing just like the same way that mylar ballons do. Most low or poor quality budget brand discs do this and start to self-rott and get spotted.

Moisture can also damage your discs because the mylar backing can corrode.

One thing to remember is check your discs at least once a year, if they are in storage. Look for spotting or anything strange. If you start to see the disc start to go bad for any reason, copy your data immediately to a new disc. Always go for quality discs, i.e. Sony, Memorex, Vebatim, TDK. A caution here though - most of these manufacturers also make low end disks so be sure the disks you are buying state that they are archival quality. You will have your own premium brand in your own locality. They will be the more expensive ones at double the price

Burning disks at a low speed will achieve a more effective and therefore more stable media write. Recordable media is much more stable than Rewritable media.

But assuming you have a USB2 port on your PC and given the very low price of an external hard drive these days, would it not be far more economical and reliable to backup to one of these?

Adopt a common sense mindset and if you are using quality media and if you adopt sensible storgae and handling practices, you would think that ten years would be a reasonable expectation. Beyond that I would start to worry.

After 20 years your optical media will be long obsolete in any case and you will have no choice but to move with the times. Such are the growing pains of technology. We will probably not be using CDs or DVDs at all then just as we have made the 3½ floppy disc obsolete.  There will cards similar to the one we use in our digital cameras that will be able to hold 100 Gigabytes or more!!!

Futher Articles

There are two considerations for an archival medium: obsolescence and durability[citation needed]. If there is no device that can read the medium, it is obsolete and the data is unavailable and thus lost.

Durability of DVDs is measured by how long the data may be read from the disc assuming compatible devices exist that can read it: that is, how long the disc can be stored until data is lost. Five factors affect durability: sealing method, reflective layer, organic dye makeup, where it was manufactured, and storage practices [29].

According to the Optical Storage Technology Association (OSTA), "manufacturers claim life spans ranging from 30 to 100 years for DVD-R and DVD+R discs and up to 30 years for DVD-RW, DVD+RW and DVD-RAM," [30] although a manufacturer of 24-karat gold-based DVDs claims lifespans of up to 300 years [31]. Of more conventional manufacturing processes, Taiyo Yuden is frequently recommended for longer durability [32].

Why archival media is hard to produce

Unlike pressed CDs/DVDs, ‘burnt’ CDs/DVDs can eventually ‘fade’, due to five things that effect the quality of CD media: Sealing method, reflective layer, organic dye makeup, where it was manufactured, and your storage practices (please keep all media out of direct sunlight, in a nice cool dry dark place, in acid-free plastic containers; this will triple the lifetime of any media).

The silver and aluminum alloys used in virtually all blank CD/DVD media has one major issue, requiring the manufacturer to lacquer a protective seal over the entire disc: silver and aluminum oxidize when they hit air, turning the normally reflective layer into silver or aluminum rust. Some (very expensive) media uses gold instead which doesn’t oxidize, however DVD media cannot use gold due to design issues (not true anymore, see update below). Today, only the cheapest of the cheap media has severe issues with sealing practices (as such, avoid any media made outside of Japan and Taiwan; especially avoid media made in India).

Assuming that the protective seal and reflective layer are manufactured correctly, the next issue is the organic dye. The first organic dyes, designed by Taiyo Yuden, were Cyanine-based and, under normal conditions, had a shelf life of around ten years; simply, that was simply unacceptable for archive discs. Taiyo Yuden, Mitsubishi Chemicals, Mitsui Co., and Ciba Specialty Chemicals spent the next ten years trying to produce the best organic dyes, eventually reaching archive-quality CD media.

Taiyo Yuden produced ‘Super Cyanine’, a chemically stabilized version of the original Cyanine dye designs, while TDK offers media that uses ‘metal-stabilized Cyanine’ dye, leading to similar shelf lives as Taiyo Yuden’s media. Taiyo Yuden states their Super Cyanine dye is chemically stable for at least 70 years, and TDK states their metal-stabilized Cyanine is also stable for 70 years.

On the other hand, Mitsubishi went in a different direction and produced what is called a Metal Azo dye, that they claim is stable for around 100 years. Azo dyes are chemically stable, however, the shelf life of media using Azo dyes typically does not exceed that of Super Cyanine and metal-stabilized Cyanine.

The third dye produced for CD media is called Phthalocyanine dye, with the majority of such dyes produced by Mitsui and Ciba. Typically marketed as more resistant to heat and UV radiation than Cyanine and Azo, modern Cyanine and Azo dyes last just as long in extreme conditions.

DVDs also use similar dyes, however manufacturers have intentionally kept what dyes they use a secret (instead of a feature in their marketing of the media), and all blank DVDs are intentionally the same color (as different dyes on CDs make blanks different colors, however, it is not indicative of what dye is used due to some manufacturers using different colored silver alloys and non-reactive additives in the dye).

There are three basic formulations of dye used in CDs & DVDs:

1. Cyanine dye CD-Rs were the earliest ones developed, and their formulation is patented by Taiyo Yuden. CD-Rs based on this dye are mostly green in color. The earlier models were very chemically unstable and this made cyanine based discs unsuitable for archival use; they could fade and become unreadable in a few years. Many manufacturers like Taiyo Yuden use proprietary chemical additives to make more stable cyanine discs ("metal stabilized Cyanine", "Super Cyanine"). Older cyanine dye based CD-Rs, as well as all the hybrid dyes based on cyanine, were very sensitive to UV-rays and could have become unreadable after only a few days if they were exposed to direct sunlight. Although the additives used have made cyanine more stable, it is still the most sensitive of the dyes in UV rays (showing signs of degradation within a week of direct sunlight exposure). A common mistake users make is to leave the CD-Rs with the "clear" (recording) surface upwards, in order to protect it from scratches, as this lets the sun hit the recording surface directly.
   
   
2. Phthalocyanine dye CD-Rs are usually silver, gold or light green. The patents on phthalocyanine CD-Rs are held by Mitsui and Ciba Specialty Chemicals. Phthalocyanine is a natively stable dye (has no need for stabilizers) and CD-Rs based on this are often given a rated lifetime of hundreds of years. Unlike cyanine, phthalocyanine is more resistant to UV rays and CD-Rs based on this dye show signs of degradation only after two weeks of direct sunlight exposure. However, phthalocyanine is more sensitive than cyanine to writing laser power calibration, meaning that the power level used by the writing laser has to be more accurately adjusted for the disc in order to get a good recording; this may erode the benefits of dye stability, as marginally written discs (with higher correctable error rates) will lose data (i.e. have uncorrectable errors) after less dye degradation than well written discs (with lower correctable error rates).
   
3. Azo dye CD-Rs are dark blue in color, and their formulation is patented by Mitsubishi Chemical Corporation. Azo dye is also chemically stable, and Azo CD-Rs are typically rated with a lifetime of decades. Azo is the most resistant dye against UV rays and begins to degrade only after the third or fourth week of direct sunlight exposure. More modern implementations of this kind of dye include Super Azo which is not as deep blue as the earlier Metal Azo. This change of composition was necessary in order to achieve faster writing speeds.

There are many hybrid variations of the dye formulations, such as Formazan by Kodak (a hybrid of cyanine and phthalocyanine).

Although the CD-R was initially developed in Japan, most of the production of CD-Rs had moved to Taiwan by 1998, and also to Mainland China, Hong Kong, Malaysia and India. Taiwanese manufacturers supplied more than 70% of the worldwide production volume of 10.5 billion CD-Rs in as of 2003.

Unfortunately, many manufacturers have added additional coloring to disguise their unstable cyanine CD-Rs in the past, so the formulation of a disc cannot be determined based purely on its color. Similarly, a gold reflective layer does not guarantee use of phthalocyanine dye. The quality of the disc is also not only dependent on the dye used, it is also influenced by sealing, the top layer, the reflective layer, and the polycarbonate. Simply choosing a disc based on its dye type may be problematic. Furthermore, correct power calibration of the laser in the writer, as well as correct timing of the laser pulses, stable disc speed, etc., is critical to not only the immediate readability but the longevity of the recorded disc, so for archiving it is important to have not only a high quality disc but a high quality writer. In fact, a high quality writer may produce adequate results with medium quality media, but high quality media cannot compensate for a mediocre writer, and discs written by such a writer cannot achieve their maximum potential archival lifetime.