Wednesday, December 14 2005 @ 10:00 AM PST
Contributed by: Richard Pitt
In this article I'm concentrating on the most typical storage medium for digital photos today, the CD/DVD.
We all use CDs - either by getting them produced from our film at the processing lab, or because we just don't have enough hard disk (or reliable enough computers) that we feel confident of keeping our precious photos safe "online".
When CD-Rs were first proposed as a consumer digital storage medium some seventeen years ago in 1988, they rode on the coattails of the original "pressed" CDs introduced a few years earlier as a distribution medium. The pressed CD is touted as having a longevity measured in centuries. The problem is, many CD-Rs we can purchase at the local computer supply store will last only from as little as a year to the typical 5-10 years; far shorter a period than most people expect. DVD-Rs (DVD-R and DVD+R) suffer from similar problems, so for now I'll lump them all in together - the only point of difference being that if you lose a DVD to age you can lose a lot more photos.
There are two major concerns with CD-R longevity: the quality of the disk to start with, and the care of the disk after recording. Both are completely in your control, but you have to understand them in order to make reasonable decisions on how or even whether to use CD-Rs for your archive.
One of the CD-Rs I created a couple of years ago now adorns my dining room side-board. Well, actually, quite a few do. They have little felt feet on them and really are drink coasters now.
The specific one I'm talking about though is one that shows extremely obvious signs that the dye layer has deteriorated; it was gold, and now is mostly green across the recorded side. The dye layer is squeezed between layers of polycarbonate (plastic) and sealed so air can't get in. Sometimes the seal breaks down; ok, lots of times the seal breaks - at least on really cheap brands of CD-Rs.
The problem is, how do you tell a good brand of CD-R from a not-so good brand?
The answer is in most cases, you can't. Even purchasing product from what appears to be reputable brand does not guarantee the disks will last more than a few years. Virtually all brands have several different quality levels, and many purchase their product from the same basic manufacturers.
There are however a few premium disks available from premium brands such as Kodak and Delkin and other well known names that in many cases come from one manufacturer that has excelled in archival media; Mitsui MAM-A. In this you should understand that I am going on information from a number of sources since to date I have not purchased these disks directly from MAM-A, only noted that there is much speculation that they are similar/the same. They all use gold as part of the bonding and imaging layer, and the most stable of the dyes, phthalocyanine. As such, you pay quite a bit more for them (2-4 times what an otherwise "normal" disk might cost).
How do these gold-containing CD-Rs (and now DVD-Rs) stack up to the competition? Well, I don't think I'll be around still by the time they are expected to deteriorate with proper handling - 300 years or so.
CD-Rs in general are fairly hardy. They are however not a single, solid piece. They are made up of several layers of plastic with a dye layer sandwiched between. The bonding of the plastic layers is where the first problems occur. If the bonding is not 100% or it opens up at some time for some reason, air and other contaminents (mold) can get in and attack the dye layer, turning it quite literally to mush - and therefore reducing the pits burned in by the laser during writing to the point of unreadability.
The dye layer is also prone to damage from light, especially sunlight, and if there is any hint of a breakdown in the seal, higher humidity will accelerate the eventual deterioration. And then of course, large or rapid changes in temperature and/or air pressure can cause the layers to separate, starting the whole process even on normally well sealed CD-Rs.
This discounts completely the problems associated with scratches on the surface of the recording side. I'm making the assumption that your archival disks will be written to and then put away safe in some fashion that means they won't be scratched and will rarely be read. If you expect to pull the disks our frequently, then I strongly suggest you write two - one for archival, and another (on cheaper media) for daily use - and recreate the daily one from the archival from time to time.
OK - so you have a number (large number?) of CD-Rs with your precious images on them and you purchased regular (not the least expensive, but not gold either) disks. What should you do?
The first thing to do is to copy the oldest disks to newer ones - even basic quality ones - as soon as you can. This includes the CDs you got from a photo lab since they don't generally use gold ones either.
Next, if you have disks that have already turned difficult to read, check to see if you have the images somewhere else - computer, friends, etc. and if not, then gather the prints (negatives if they were traditional film) together so you have a chance to scan them if you feel it necessary. Remember, real film is best - but it has its own storage problems: acid free sleeves (or polyethylene or polypropylene today) stored in a steel cabinet or acid-free box in a place that doesn't get hot in the summer or high humidity any time.
You might want to get one of the large external hard drives (USB or FireWire connection) to facilitate copying and arranging images prior to "real" archiving. The reason is that most of us don't get anywhere near as many images onto a CD-R as they can hold, so we end up with lots of CDs with only a few pictures on them. With several hundred Gigabytes of hard disk space, you can more easily combine them onto a smaller number of well-packed disks - and even reduce bunches of CD-Rs to DVD-Rs for even better savings. I'll deal with why and how to do this in another article - but for now, you can simply "drag and drop" the contents of each CD-R to the hard drive and then use the software you got with your CD/DVD writer to make up new CDs with aggregates of the data from the originals.The one thing to note at this point is - Don't Use Compression!" The images from most cameras are already compressed so it is a waste of time doing it, and it adds a potential for not being able to read the disk later in another computer that might not know how to uncompress it properly.
If you still have disks that can't be fully read, you might want to ask one of your more technically savvy friends to try on their computer - with a different disk drive. Sometimes newer drives can read bad disks, and sometimes older ones can - there are subtle differences in the way they read and how many times they'll try to re-read a bad segment of data. Be persistent.
If you still can't read the disk - move on and remember - and don't let it happen again.